I'm on Ubuntu GNU/Linux 21.10 with the latest installation of Zoom, version 5.9.3 (1911).
When I start a meeting, if I don't have a microphone or headset attached, Zoom attempts to detect the microphone repeatedly, causing a huge number of pop-up windows and on-screen messages that say "Zoom cannot detect your microphone". See the attached image (with sensitive information removed).
Essentially Zoom desktop is not usable in the latest version on Ubuntu GNU/Linux.