Raising the target SDK just turns a general computing device into a glorified webbrowser, because you lose access to the filesystem, the ability to run background daemons, and the ability to run compilers.
These should be permissions, not disabled wholesale.
Literally the only situation when an app would need access to your filesystem is when the app is a file manager. And file managers can still request access to your file system.
Not at all. If you want to support e.g. playlists you need to be able to load video files while the storage framework only gives you access to the playlist file.
Or when you want to store and load ROMs from a folder.
Or in general every time you want to automatically load files that should also be accessible to other apps.
Unsure why you think the storage access framework doesn't let you grant access to a directory. You can literally try it on a relatively modern app such as Lemuroid: the system file picker lets you grant access to your ROMs folder.
Whole access to the shared storage is deprecated by SAF and scoped storage. That doesn't mean there is no way to achieve the same productivity tasks you could achieve before: it's just that now you're granting explicit fine-grained access to the files and folders your app needs.
MANAGE_EXTERNAL_STORAGE still exists and is now reserved for apps that can justify their file management purpose. Since this is a highly privacy-invasive permission, Play Store requires a review for these kinds of apps.
These should be permissions, not disabled wholesale.