I have made this, and have been using it for some months now. I have been doing and testing new things. GitHub - alexjp/activities_work
Basically, currently activities do not isolate any kind of “files or folders”. My goal was to isolate some files/folders for apps in activities, and it rather works very well.
There are currently 3 ways I tested it with, and all mostly work pretty well. I settled with bwrap, since its how flatpak works, and flatpak is pretty common.
The goal was to, say you have a personal activity and a work activity, and have personal and work emails, the email client on the personal activity would only have your personal emails, and the work activity would have the work emails.
It rather works very well, currently I even have activities for specific code environments with its own browser profiles/IDE settings and code.