Protocols, not platforms, people!
Therefore even if your chat log is leaked by one member, it isn't possible to probe person A sent the message. If person B was the leaker, anyone that person B has ever communicated with on Signal could have sent the message appearing to be from person A.
Not sure when you last looked at the landscape.
Servers: Synapse, dendrite, conduit
Clients: (just off the top of my head)
Element, fluffychat, cinny, neochat, cyphon, nheko, schildichat
Clients outside mobile OSes are not interesting if you are considering Signal replacements. On mobile, you have element and maybe fluffychat.
It is still a messaging thingie that lacks a decent server implementation, and lacks a good client app.
If you want all the voip bits in place and all the latest features, you have to run a specific combination of synapse, sliding-proxy and element as the client. The xmpp ecosystem has similar problems but it gives a bit more leeway with various combinations of servers and clients that work well.
Matrix has more focus on IRC-like rooms, has a lot more features for that purpose and is much nicer to use than any conference xmpp extension.
https://matrix.org/ecosystem/servers/
The designers of matrix decided to shift more of the burden of the protocol to the server so that clients would be easier to implement. Therefore there are few servers and many clients. e2ee makes the client more complicated, that's why not all clients support e2ee