@AbbieNormal I don't know (maybe it's optional?); on Element/Matrix you can have it. Anyway the problem is not only with groups, it's with claiming "we can't possibly read your contents when they are end-to-end encrypted", while they easily can, when using their web sites.

@AbbieNormal
I think they all are not trustworthy, in particular since they claim they offer "end-to-end encryption": https://bu.noblogs.org/end-to-end-encryption-security-and-the-web/

@sophie the possibility to mark a message as silent (as in "in any case this won't make the receivers' devices emit any sound") before sending it would be great, and I think it would also be easy to implement in any client.