We just used Microsoft Teams (which I imagine isn't remotely
free, but our work IT department is obsessed with Microsoft).
It was moderately OK, has an unbelievably annoying linux
version: For instance, you can't ever exit, it keeps running forever till
you find it and kill it with extreme prejudice, it insists on
being full screen, but doesn't position the window at (0,0),
it pops up new chat notifications directly on top of the area
you are trying to type in, etc.
FWIW I've been using Teams from chrome on Fedora 30 for like two weeks now for classes (audio, video, chat and screen sharing), and, touch wood, it's been very stable.
[Sorry for the html, I'm typing this on my phone.]