Earlier quoted context omitted.
Jitsi Meet. It doesn't require any account or installation. Just create a room and share the link or room name. https://meet.jit.si There is also a Jitsi app available for mobile devices, but it is optional.
I really like Jitsi. But. In a thread about a Signal outage with a request for an alternative "casual messaging" app - I really don't think open source video video meetings is a relevant answer...
I must have misread it as "casual meeting", like a simple way to set up an online meeting.