HI, Thanks for the info (and also thanks to PoVog).

My experience with mqtt is limited. I once set up a ejabberd server to try it out. It works but -as I mainly interested in federated chat- it was not that interesting. There was a lot less traffic and the rooms that exist that had traffic had a big issue with moderation (i.e. spam content). The S/N ratio of the discussions was a lot less then on matrix or other platforms.

I also notice it was missing some features that are do are present in matrix, like the ability to edit messages. From how I understand it, the modulator nature of XMPP is a nice idea but as there is a large diversity on clients and the features they support, it does seems to come down to only the lowest common domininator to really work well.

As I have just set up a pi5 as my new selfhosting-server, I might give it a try again, and see how well the transports (like slidge as mention by PoVog) work.

Concerning the URL issue, as explained, it kind-of looks like a normal side-effect of the principle of server authentication. Alsom your use-case (one server, one client) it not the normal goal why chat-servers are build. Even in a non-federated use, you have multiple clients connecting to it. Cchanging the server hostname will impact all clients, so is probably a very rare scenario. I did see you use synapse. I do not know if you dendrite or conduit have the same behaviour.