There's a lot of discussion here about key exchange, and how you need to trust whatever service is managing the keys. From the demo, it looks like the key is basically a password. If you can share the password out-of-band through another secure channel (perhaps post it in a Signal chat or something), then your meeting should be secure. It can even be included as part of the link.
But then doesn't the Jitsi web server have to access password when you enter it on their website/have it in the link? Nope! It looks like they're putting the password in an anchor fragment in the URL, which is not sent to the web server [1]. So all encryption/decryption is being done client side (and is therefore real end-to-end encryption).
Yes, it's possible the web server is sending you evil JavaScript that is extracting your password anyway, but at least that's something you can in principle check. For all end-to-end encryption to work, you have to know your client is not compromised.