Ship an appimage or something, use basic fs abstraction to create an encrypted blob, do whatever you want within said blob.

Look at virtualbox or something for inspiration.

Look at xdg desktop portals for transfering files.

What kind of privacy are you after?

AVs in Linux realm exist mostly for scanning windows stuff for email attachments, shared storage, etc.

Worry not! The horse in this case is them. You can show them a better way, but can’t force them to take it :)

One can bring horse to water.

Devs are usually technical enough to understand privacy. Have you tried suggesting a switch to matrix or simplex?

I doubt it’s much more privacy respecting, but google(?) did have its ingress game.