Webform states submodule does not work.

Can you provide some more information on the circumstances under which this isn't working? We have a test that enables the submodule, installs a webform and then executes a query to retrieve all kinds of states, and then checks that the correct information is returned. It's all working as expected in the test.

I verified the Type plugins and they are namespaced correctly, so they should be automatically discovered by the plugin manager, as long as the module is enabled. The plugins being located in the main module or the submodule shouldn't matter. They are loaded by GraphQL's TypePluginManager which uses the standard discovery mechanism from Drupal core.

Just to be sure, could you verify that the submodule is enabled?

I am not sure about the exact circumstances.
The main and submodule are enabled. But I keep getting:
LogicException: Missing type WebformElementStates. in Drupal\graphql\Plugin\GraphQL\Schemas\SchemaPluginBase->getType() (line 421 of /app/docroot/modules/contrib/graphql/src/Plugin/GraphQL/Schemas/SchemaPluginBase.php)

And for me it's working fine when I merge the sub and the main module.
I know it is odd.

Sorry figured it out there was a placeholder module in our custom modules that has overridden the submodule.
Ticket can be closed as works as designed :facepalm: