Here's another related question - Granting an app access to only a specific file or folder, through the system file chooser (is that the right term?), apparently grants perpetual access to that file or folder, and then there's nowhere in settings to go to manage that.
Steps:
Open an app (a file sharing app, for instance). Click upload folder. The system file picker comes up. Click on a folder and click "Use this folder." A dialog comes up saying "Allow [app name] to access files in [folder name]? This will let [app name] access current and FUTURE content stored in [folder name]." Click grant, the app does its thing and uploads the folder, but then I can't figure out where to manage that access.
It's not in App Info (Permissions makes it look like there's no storage access, and in Storage Scopes I've given access to a directory but not the one in question). A search in Settings for "files" does not turn up that app at all in "all files access."
So.. apparently the app just has perpetual access to that folder now?