[zertrin]

Yeah in E2EE key distribution is always the tricky part.

For "good" UX, usually it is based on trust that the peer keys are exchanged with help of the centralised service as middle man but that it does not alter the keys.

For good security, each party should ideally check public key fingerprints with each other party via another mean of communication to ensure that there was no man in the middle. But that's poor UX and might be unpractical for large meetings of participants that do not know each other.