I use flatpak steam and flatseal to remove user home permissions so games don't see my files.
I'd prefer to use Nix derivations and firejail but I couldn't get it working last time I tried.
My preference for nix expressions to flatpaks is for better reproducibility guarantees, easier introspection, easier debugging, and less duplication.
Not for android, but I use this for PC:
https://github.com/jamesmcm/vopono