Why does Android 11 have restrictions File Manager?

The reason while the android 11 OBB folder was restricted from being accessed was due to the fact that android wanted to stop files from interacting with each other , basically separating them in a container, while also stopping the user from manually making changes to files or app data.

Change app permissions

Change permissions based on their type

To locate the Permission Manager, open the Settings app and then tap Privacy. In the resulting window, tap Permission Manager.