Not signal specifiaclly, but they said they would shutter operations in the uk if the online “safety” bill passed. @neil@mastodon.neilzone.co.uk has posted a lot about it.
The vpn, sure, but if you host it on a vps (and don’t make it public) then all of the requests are coming from the vps’s ip. This is private, but not anonymous.
The backend isn’t open source. Iirc, its just the clients.