Which version are you using right now? I have the latest one and it does not allow me to share anything else than a white canvas.
Do you launch zoom somehow differently? For me it behaves like a regular XWayland app
With the previous version I had the same thing, only allowed me to share white canvas.
Here's the process hierarchy:
\_ gdm-session-worker [pam/gdm-password]
\_ /usr/libexec/gdm-wayland-session gnome-session
\_ /usr/libexec/gnome-session-binary
\_ /usr/bin/gnome-shell
\_ /usr/bin/zoom
\_ sh -c export SSB_HOME=/home/me/.zoom; export QSG_INFO=1; export LD_LIBRARY_PATH=/opt/zoom; /opt/zoom/zoom ""
\_ /opt/zoom/zoom