Try a different browser. On Mac, Safari is much more resource efficient than Chrome for example. On Windows I'm not sure, but it can't hurt t give FF a try.
Last I checked FF was not even supported :)
Looks supported now
It has been supported for at least a month, probably two. I didn't (have to) use Zoom before that, thankfully.
N=1, but it works great in Firefox on Linux and doesn't use noticeably more resources that what I usually see with video calls.
Haven't had this problem. And in general, we try to get people to use whereby (also the web version), which we've been very happy with.