I also disagree with your opinion that "you can't solve the UX on that". The tech demo here essentially gives the same UX as Zoom call + passwords, but with actual end-to-end encryption.
There is the notable caveat in this tech demo that client-side scripts can still read the key (we have to assume the javascript that can read the URL hash is friendly).
Really, though, this can be solved: provide a native(ish) app even if it's just an Electron wrapper of the existing static assets and javascript code, register a handler with the OS for `jitsi://`, and use links like `jitsi://server.name/room#e2ekey=foo`, so we only have to trust the code on our machine, not the server.