TYPO3 Core

Confirmed, same issue here.
Maybe as a workaround you could define that default parameters in the yaml site config and nullify them, while disabling the skipDefaultArguments option.
I'll be testing that later on.

Tested:
You can remove the default Controller/Action with this additional route. In my case it's the list Action of the Project controller.

- { routePath: '', _controller: 'Project::list' }

Robert Vock wrote:

When I set config.tx_extbase.features.skipDefaultArguments = 1 in TypoScript, then the controller-parameter will not appear in the $parameters, when it's the default controller for the plugin. When applyControllerActionValues gets called, it overwrites the current action of the parameters-array with the default action.

Relevant code positions:
ExtbasePluginEnhancer.php#L117
ExtbasePluginEnhancer.php#L216

Out of curiosity, could this be related to https://docs.typo3.org/m/typo3/reference-coreapi/master/en-us/ApiOverview/Routing/AdvancedRoutingConfiguration.html?highlight=slug#extbase-plugin-enhancer ? To be specific, the explicit shown warning.

You're right. When I wrote this bug report, that documentation didn't exist. I only had the Feature description: https://docs.typo3.org/c/typo3/cms-core/master/en-us/Changelog/9.5/Feature-86365-RoutingEnhancersAndAspects.html

I guess you can close this report or update the enhancer to respect the defaultController.