Is there any way to trigger some task when a GitHub action is “installed”, or more usefully when its “uninstalled” (workflow removed)?
Is there any feedback?
No. GitHub Actions aren’t installed or uninstalled, they’re simply used as part of a workflow or not.
There’s no way for you, as an author of an action, to know when someone has added or removed your action to a workflow.
Even if an action is not formally “installed”, I really think there is some process triggered when it’s first detected, and when it’s no longer, as for the scheduling that only run while the action is there.