Zoom's whiteboard is pretty bad. Slow, clunky, weird bugs on some OSes (pen draws in wrong place on Android IME), no pressure sensitivity. There are loads of shared whiteboard type services (search on HN; IIRC we've had a few discussions recently), but most of them don't support audio and video as well. I think Zoom for audio and video while using a separate shared whiteboard might work quite well, but I haven't had reason to try it yet.