I don't know about the number of participants, luckily I've never been in a mammoth call. As for the background blur, it may be related to a missing feature in Electron. I seem to remember that another conferencing app (might have been zoom, not sure) didn't support this while running on Chrome/Linux, so I figure it's related.
To me, the main missing feature on Linux is the "native notifications" feature (as opposed to the bespoke window that pops up).