If you really only want group calls for a handful of people I can only recommend Signal for that. Just create a group chat in there. You can start a call and select it to not ring on the other peoples end and then you can just hop in and out just like a discord vc. It has a desktop app for Mac/Linux/Windows too so you could use it while gaming too. The app is not pretty but it’s minimalistic and it works. Everything is end to end enrypted even the calls and video calls.

You could even screenshare with it but i never tested how well that works. It’s free and open source. It is not federated however. But still the most easy to use and best secure and private messenger out there.