What do you need screen sharing for? This comes up so, so rarely for me.
Besides the expensive Matrix option the parent suggested, IRC covers text fine. Mumble handles low-latency, low-resource voice chat with positional audio for games. XMPP uses more resources that IRC (but can have encryption) but a ton less resources than Matrix which makes it suitable for self-hosting—my partner & I do voice/video calls over my home server fine & Movim is working on group calls with a Web UI (tho it should be noted both Zoom & Jitsi use XMPP under the hood).
Well Discord, Slack, & others are web tech too so it’s not like avoiding it is easy. If I have to use these services, I would prefer it be in the browser’s sandbox.
Even still, almost all debug, troubleshoot, pairing session I have done in the last 4 years have been done over Upterm or Tmate, which is much, much lighter on bandwidth & not crushed by video compression.