2.PC / Laptop as a projector source?

Hi, I have in my room 2 PC, My main pc and a 2.PC. I want to connect to my 2.PC a beamer and then control of my main PC, is that possible? Except with teamviewer or something. (Both PC have Linux mint 19.2)

Teamviewer would be safe. If you prefer an opensource solution and spend some time then VNC an option. Look here:

https://wiki.ubuntuusers.de/VNC/

I tried it last night with vnc server, and I think that's a sensible solution.