Well, it seems that screen sharing is indeed not working properly for you. It is strange, I don’t think it should require any additional permissions on Linux and it was tested on Ubuntu and Debian (I am personally using Debian Linux all the time). What particular version of Ubuntu are you using?
Also, it would be really helpful if you send us terminal output from FarPlay when you start screen sharing. All you need for this is to run FarPlay from a terminal (open Terminal app and run farplay command there; then start a session, open video and start screen sharing). Then just select all and copy the content of the terminal window (it may be lengthy but it’s ok).
