Installed Signal, wanted to use it. First step is to connect with my phone number and there is no other way to create an account. This is an unfortunate privacy-blind choice for what otherwise could be a great platform.
It's probably somebody from the "Usernames are bad UX and if we have bad UX nobody will use the messanger and then we don't actually get a secure messenger because we don't get a messenger that anybody uses at all"-camp".
You can still register with some landline or VoIP number if you want.