Rando

Second this, me and my friends have been using it since the day it came out (I am the one hosting it) and it checks all the boxes for us.

I was never able to get my group to switch away from Discord but this has finally done it

One Linux you could, I.E. for a flatpak you could use flatseal (or manually do it via command line) to lock down what folders the flatpak can operate in. I just did this for Brave Browser.

There is also the software Bubblewrap that accomplishes the same. These are at the application level for the entire browser though.

There is so many in the world it is actually crazy