That just means that the x-mime is not known. You will need to add this to your Desktop file. I guess it is this one:
/usr/share/applications/Zoom.desktop
Copy it to your home folder:
cp /usr/share/applications/Zoom.desktop ~/.local/share/applications/Zoom.desktop
and add there:
MimeType=x-scheme-handler/zoommtg
then
update-desktop-database ~/.local/share/applications/
and check if it is in the list:
cat ~/.local/share/applications/mimeinfo.cache
In general it should work then.