They don't like forks using their servers, but it's the users who connect to their servers, not the fork publisher. Those users are permitted to connect via the TOS, which is independent from the GPL.
This is the problem in my mind. Open source in words, but not spirit.
https://github.com/signalapp/Signal-Android/issues/11101#iss...
Among the official reasons given was staying ahead of spammers. In this instance it was also speculated that the payment function which they were building into the server was to remain secret.
https://github.com/signalapp/Signal-Android/issues/11101#iss...
The openness or otherwise of the code has literally nothing to do with the terms of use of any service being run.
The product _is_ the network. By restricting access to the network, access to the product is also curtailed.
So what's your point? Do you think everyone should have a right to connect to their servers however they like, and the service operator can't exert any control over that?
Signal is not federated, as an explicit design decision.
The source code for the server and the client are both free software.
If this isn't true, I'd be very interested to learn more.