'minifyhtml' is not a supported key.

Tried to reproduce this with 10.2.3 and 10.2.4 and it works for both. There must be something specific to your site that is causing the issue.

Ping me on the #minifyhtml slack channel if you want to look into it more.

The same error:

'minifyhtml' is not a supported key.

appeared on the Home > Administration > Configuration > Development page today while maintaining one of our sites.

Additional notes about the problem described above:

After uninstalling drupal/minifyhtml (2.0.4) and removing the drupal/minifyhtml code from the project ...

The error regarding - 'minifyhtml' is not a supported key - still appears (see screenshot on drupal slack)

[composer update run, showing drupal/minifyhtml removal]

vendor/bin/drush state:set system.maintenance_mode 1
composer.phar update --with-all-dependencies
Loading composer repositories with package information
Updating dependencies
Lock file operations: 0 installs, 2 updates, 4 removals
  - Removing drupal/minifyhtml (2.0.4)
  - Removing drupal/minifyjs (3.0.1)
  - Removing matthiasmullie/minify (1.3.73)
  - Removing matthiasmullie/path-converter (1.1.3)
  - Upgrading mglaman/phpstan-drupal (1.2.7 => 1.2.8)
  - Upgrading phpstan/phpdoc-parser (1.26.0 => 1.27.0)
Writing lock file
Installing dependencies from lock file (including require-dev)
Package operations: 0 installs, 2 updates, 4 removals
  - Downloading mglaman/phpstan-drupal (1.2.8)
  - Downloading phpstan/phpdoc-parser (1.27.0)
  - Removing matthiasmullie/path-converter (1.1.3)
  - Removing matthiasmullie/minify (1.3.73)
  - Removing drupal/minifyjs (3.0.1)
  - Removing drupal/minifyhtml (2.0.4)
  - Upgrading mglaman/phpstan-drupal (1.2.7 => 1.2.8): Extracting archive
  - Upgrading phpstan/phpdoc-parser (1.26.0 => 1.27.0): Extracting archive
Deleting /modules/minifyjs/ - deleted
Deleting /modules/minifyhtml/ - deleted
Generating autoload files
> Drupal\Core\Composer\Composer::preAutoloadDump
vendor/bin/drush -n -y updb
[success] No pending updates.
vendor/bin/drush -n -y cr

Not sure what's causing this. We have it installed on a multi site system and on one of the sites we were getting this message when trying to enable css/js aggregation.

Even after uninstalling the module we still had the issue.

An export and search of the sites config found the following entries in the system.performance.yml file.

minifyhtml:
minify_html: 0

I did a single file export of system.performance.yml, removed the minify_html settings from the file and did an single file import and was able to enable css/js aggregation.

I had the same problem on Drupal 10.3, on a site that didn't have Minifyhtml installed anymore for a long time, but the lines
minifyhtml:
minify_html: 0
did not get removed from system.performance.yml whenever the module was uninstalled. As a result the perfomance page could not be saved until I edited the yml file directly and imported the config.