If you are hosting webinars there's also bigbluebutton
Unlike the alternatives at the time from Google, Apple, etc., it didn't require an account for participants — I could just give them the meeting room URL. So although it wasn't open source, it at least didn't lock you into a network.
(Unlike you, I wasn't up for self-hosting.)
But you can see:
> Powered by [LiveKit](https://livekit.io/)
Fine since this is an open source product, but not full EU sovereignty of the software stack.
Livekit could at any time change their license and drop support for the free open-source version like so many products have done in the past.
If a EU entity forks it and maintains it, then that'd be end-to-end sovereignty IMO.
The chat seems extremely basic, so not really an alternative if you need chat with e.g. message edit/delete/formatting/pictures as well as video/audio.