you can lock meetings that has started
this is not a UX issue, it is people who give no fuck about security of privacy
otherwise your government would have voted anti data-spying laws, they haven't therefore they don't care, therefore they didn't think of locking their meeting after it started
i can spell the agenda that's cooking
https://blog.zoom.us/keep-uninvited-guests-out-of-your-zoom-...
https://support.zoom.us/hc/en-us/articles/201362603-Host-and...