Error: Class "Drupal\bat_roomify\EventFormatter\AbstractEventFormatter" not found

Had a quick look at this, I don't think its simple as adding dependencies because bat_roomify is showing as only being compatible with ^D11

We may need a maintainers input for intended usage.

is bat_roomify enabled?

bat_roomify is not enabled, as it is not compatible with 10.4.4

For some reason Composer only installs alpha3, not alpha6.

You can refer to this tested install process
https://www.drupal.org/docs/extending-drupal/contributed-modules/contrib... →

"For some reason Composer only installs alpha3, not alpha6."

check your composer.json

solution@s031 [~/public_html/epicure.club]# vendor/drush/drush/drush updb
[warning] Invalid json in modules/contrib/bat/composer.json
[success] No pending updates.
[error] Error: Class "Drupal\bat_roomify\EventFormatter\AbstractEventFormatter" not found in include() (line 14 of /home/solution/public_html/epicure.club/web/modules/contrib/bat/modules/bat_fullcalendar/src/FullCalendarFixedStateEventFormatter.php) #0 /home/solution/public_html/epicure.club/vendor/composer/ClassLoader.php(576): include()
#1 /home/solution/public_html/epicure.club/vendor/composer/ClassLoader.php(427): Composer\Autoload\{closure}('/home/solution/...')
#2 [internal function]: Composer\Autoload\ClassLoader->loadClass('Drupal\\bat_full...')
#3 /home/solution/public_html/epicure.club/vendor/symfony/dependency-injection/ContainerBuilder.php(1131): ReflectionClass->__construct('Drupal\\bat_full...')
#4 /home/solution/public_html/epicure.club/vendor/symfony/dependency-injection/ContainerBuilder.php(586): Symfony\Component\DependencyInjection\ContainerBuilder->createService(Object(Symfony\Component\DependencyInjection\Definition), Array, true, 'bat_fullcalenda...')
#5 /home/solution/public_html/epicure.club/vendor/symfony/dependency-injection/ContainerBuilder.php(531): Symfony\Component\DependencyInjection\ContainerBuilder->doGet('bat_fullcalenda...', 1)
#6 /home/solution/public_html/epicure.club/web/modules/contrib/bat_api/src/Plugin/ServiceDefinition/CalendarEventsIndex.php(122): Symfony\Component\DependencyInjection\ContainerBuilder->get('bat_fullcalenda...')
#7 /home/solution/public_html/epicure.club/web/core/lib/Drupal/Core/Plugin/Factory/ContainerFactory.php(21): Drupal\bat_api\Plugin\ServiceDefinition\CalendarEventsIndex::create(Object(Drupal\Core\DependencyInjection\ContainerBuilder), Array, 'calendar_events...', Array)
#8 /home/solution/public_html/epicure.club/web/core/lib/Drupal/Component/Plugin/PluginManagerBase.php(83): Drupal\Core\Plugin\Factory\ContainerFactory->createInstance('calendar_events...', Array)
#9 /home/solution/public_html/epicure.club/web/modules/contrib/services/src/Entity/ServiceResource.php(162): Drupal\Component\Plugin\PluginManagerBase->createInstance('calendar_events...', Array)
#10 /home/solution/public_html/epicure.club/web/modules/contrib/services/src/Routing/ServiceEndpoint.php(23): Drupal\services\Entity\ServiceResource->createServicePluginInstance()
#11 [internal function]: Drupal\services\Routing\ServiceEndpoint->routes()
#12 /home/solution/public_html/epicure.club/web/core/lib/Drupal/Core/Routing/RouteBuilder.php(146): call_user_func(Array)
#13 /home/solution/public_html/epicure.club/web/core/lib/Drupal/Core/ProxyClass/Routing/RouteBuilder.php(83): Drupal\Core\Routing\RouteBuilder->rebuild()
#14 /home/solution/public_html/epicure.club/web/core/includes/common.inc(485): Drupal\Core\ProxyClass\Routing\RouteBuilder->rebuild()
#15 /home/solution/public_html/epicure.club/vendor/drush/drush/src/Commands/core/UpdateDBCommands.php(87): drupal_flush_all_caches()
#16 [internal function]: Drush\Commands\core\UpdateDBCommands->updatedb(Array)
#17 /home/solution/public_html/epicure.club/vendor/consolidation/annotated-command/src/CommandProcessor.php(276): call_user_func_array(Array, Array)
#18 /home/solution/public_html/epicure.club/vendor/consolidation/annotated-command/src/CommandProcessor.php(212): Consolidation\AnnotatedCommand\CommandProcessor->runCommandCallback(Array, Object(Consolidation\AnnotatedCommand\CommandData))
#19 /home/solution/public_html/epicure.club/vendor/consolidation/annotated-command/src/CommandProcessor.php(175): Consolidation\AnnotatedCommand\CommandProcessor->validateRunAndAlter(Array, Array, Object(Consolidation\AnnotatedCommand\CommandData))
#20 /home/solution/public_html/epicure.club/vendor/consolidation/annotated-command/src/AnnotatedCommand.php(387): Consolidation\AnnotatedCommand\CommandProcessor->process(Object(Symfony\Component\Console\Output\ConsoleOutput), Array, Array, Object(Consolidation\AnnotatedCommand\CommandData))
#21 /home/solution/public_html/epicure.club/vendor/symfony/console/Command/Command.php(326): Consolidation\AnnotatedCommand\AnnotatedCommand->execute(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#22 /home/solution/public_html/epicure.club/vendor/symfony/console/Application.php(1096): Symfony\Component\Console\Command\Command->run(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#23 /home/solution/public_html/epicure.club/vendor/symfony/console/Application.php(324): Symfony\Component\Console\Application->doRunCommand(Object(Consolidation\AnnotatedCommand\AnnotatedCommand), Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#24 /home/solution/public_html/epicure.club/vendor/symfony/console/Application.php(175): Symfony\Component\Console\Application->doRun(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#25 /home/solution/public_html/epicure.club/vendor/drush/drush/src/Runtime/Runtime.php(110): Symfony\Component\Console\Application->run(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#26 /home/solution/public_html/epicure.club/vendor/drush/drush/src/Runtime/Runtime.php(40): Drush\Runtime\Runtime->doRun(Array, Object(Symfony\Component\Console\Output\ConsoleOutput))
#27 /home/solution/public_html/epicure.club/vendor/drush/drush/drush.php(139): Drush\Runtime\Runtime->run(Array)
#28 /home/solution/public_html/epicure.club/vendor/drush/drush/drush(4): require('/home/solution/...')
#29 {main}.
Error: Class "Drupal\bat_roomify\EventFormatter\AbstractEventFormatter" not found in include() (line 14 of /home/solution/public_html/epicure.club/web/modules/contrib/bat/modules/bat_fullcalendar/src/FullCalendarFixedStateEventFormatter.php).
[warning] Drush command terminated abnormally.

Alpha 7 has support for bat_roomify on Drupal 10.2 on

https://www.drupal.org/project/bat/releases/11.1.0-alpha7 →

I can confirm that Alpha7 allows installation on 10.4.4.

The bat_roomify error remains:

[error] Error: Class "Drupal\bat_roomify\EventFormatter\AbstractEventFormatter" not found in include() (line 14 of /home/solution/public_html/epicure.club/web/modules/contrib/bat/modules/bat_fullcalendar/src/FullCalendarFixedStateEventFormatter.php) #0 /home/solution/public_html/epicure.club/vendor/composer/ClassLoader.php(576): include()
#1 /home/solution/public_html/epicure.club/vendor/composer/ClassLoader.php(427): Composer\Autoload\{closure}('/home/solution/...')
#2 [internal function]: Composer\Autoload\ClassLoader->loadClass('Drupal\\bat_full...')
#3 /home/solution/public_html/epicure.club/vendor/symfony/dependency-injection/ContainerBuilder.php(1131): ReflectionClass->__construct('Drupal\\bat_full...')
#4 /home/solution/public_html/epicure.club/vendor/symfony/dependency-injection/ContainerBuilder.php(586): Symfony\Component\DependencyInjection\ContainerBuilder->createService(Object(Symfony\Component\DependencyInjection\Definition), Array, true, 'bat_fullcalenda...')
#5 /home/solution/public_html/epicure.club/vendor/symfony/dependency-injection/ContainerBuilder.php(531): Symfony\Component\DependencyInjection\ContainerBuilder->doGet('bat_fullcalenda...', 1)
#6 /home/solution/public_html/epicure.club/web/modules/contrib/bat_api/src/Plugin/ServiceDefinition/CalendarEventsIndex.php(122): Symfony\Component\DependencyInjection\ContainerBuilder->get('bat_fullcalenda...')
#7 /home/solution/public_html/epicure.club/web/core/lib/Drupal/Core/Plugin/Factory/ContainerFactory.php(21): Drupal\bat_api\Plugin\ServiceDefinition\CalendarEventsIndex::create(Object(Drupal\Core\DependencyInjection\ContainerBuilder), Array, 'calendar_events...', Array)
#8 /home/solution/public_html/epicure.club/web/core/lib/Drupal/Component/Plugin/PluginManagerBase.php(83): Drupal\Core\Plugin\Factory\ContainerFactory->createInstance('calendar_events...', Array)
#9 /home/solution/public_html/epicure.club/web/modules/contrib/services/src/Entity/ServiceResource.php(162): Drupal\Component\Plugin\PluginManagerBase->createInstance('calendar_events...', Array)
#10 /home/solution/public_html/epicure.club/web/modules/contrib/services/src/Routing/ServiceEndpoint.php(23): Drupal\services\Entity\ServiceResource->createServicePluginInstance()
#11 [internal function]: Drupal\services\Routing\ServiceEndpoint->routes()
#12 /home/solution/public_html/epicure.club/web/core/lib/Drupal/Core/Routing/RouteBuilder.php(146): call_user_func(Array)
#13 /home/solution/public_html/epicure.club/web/core/lib/Drupal/Core/ProxyClass/Routing/RouteBuilder.php(83): Drupal\Core\Routing\RouteBuilder->rebuild()
#14 /home/solution/public_html/epicure.club/web/core/includes/common.inc(485): Drupal\Core\ProxyClass\Routing\RouteBuilder->rebuild()
#15 /home/solution/public_html/epicure.club/vendor/drush/drush/src/Commands/core/UpdateDBCommands.php(87): drupal_flush_all_caches()
#16 [internal function]: Drush\Commands\core\UpdateDBCommands->updatedb(Array)
#17 /home/solution/public_html/epicure.club/vendor/consolidation/annotated-command/src/CommandProcessor.php(276): call_user_func_array(Array, Array)
#18 /home/solution/public_html/epicure.club/vendor/consolidation/annotated-command/src/CommandProcessor.php(212): Consolidation\AnnotatedCommand\CommandProcessor->runCommandCallback(Array, Object(Consolidation\AnnotatedCommand\CommandData))
#19 /home/solution/public_html/epicure.club/vendor/consolidation/annotated-command/src/CommandProcessor.php(175): Consolidation\AnnotatedCommand\CommandProcessor->validateRunAndAlter(Array, Array, Object(Consolidation\AnnotatedCommand\CommandData))
#20 /home/solution/public_html/epicure.club/vendor/consolidation/annotated-command/src/AnnotatedCommand.php(387): Consolidation\AnnotatedCommand\CommandProcessor->process(Object(Symfony\Component\Console\Output\ConsoleOutput), Array, Array, Object(Consolidation\AnnotatedCommand\CommandData))
#21 /home/solution/public_html/epicure.club/vendor/symfony/console/Command/Command.php(326): Consolidation\AnnotatedCommand\AnnotatedCommand->execute(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#22 /home/solution/public_html/epicure.club/vendor/symfony/console/Application.php(1096): Symfony\Component\Console\Command\Command->run(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#23 /home/solution/public_html/epicure.club/vendor/symfony/console/Application.php(324): Symfony\Component\Console\Application->doRunCommand(Object(Consolidation\AnnotatedCommand\AnnotatedCommand), Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#24 /home/solution/public_html/epicure.club/vendor/symfony/console/Application.php(175): Symfony\Component\Console\Application->doRun(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#25 /home/solution/public_html/epicure.club/vendor/drush/drush/src/Runtime/Runtime.php(110): Symfony\Component\Console\Application->run(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#26 /home/solution/public_html/epicure.club/vendor/drush/drush/src/Runtime/Runtime.php(40): Drush\Runtime\Runtime->doRun(Array, Object(Symfony\Component\Console\Output\ConsoleOutput))
#27 /home/solution/public_html/epicure.club/vendor/drush/drush/drush.php(139): Drush\Runtime\Runtime->run(Array)
#28 /home/solution/public_html/epicure.club/vendor/drush/drush/drush(4): require('/home/solution/...')
#29 {main}.

Had same error on a existing Drupal 10, disappeard after drush en bat_roomify.

The drush command in #14 did the trick. Surprising, as bat_roomify was already enabled...

Thank you Augusto

Good to ear that!