Not federated, but definitely anonymous. All Signal messages are E2EE, and Signal can’t even access your messages. They literally have a page where they list every time they’ve been asked by the government to give info, and they can’t. https://signal.org/bigbrother/

Right in the Signal box, it says “Or Matrix/XMPP”. It’s super tiny for some reason.

Also, I recommend using Chris Titus Tech’s winutil program to disable Telemetry and install some programs (you can even uninstall Edge and the Store, but not recommended)

https://github.com/ChrisTitusTech/winutil