Session is what you want. But you have to directly shares each others public keys to connect

They implemented an alt method IIRC but you must go out of your way to search and find it. I just recall seeing a bunch of post headlines about using email or something like that a year or so back.

They send an initial SMS message that is a main expense and funded by some rich person and donations. I think that has some significance to encryption or something but I'm not sure of the details. I could be wrong on that one, it has been years since I read the details.

thousands of threads on this topic since decades ago.

it's an eternal debate (since signal has no plans to change)

just read the history and join the rest of us waiting for them to change. using signal before that change is completely optional. go ahead and don't use it. no problem.

opening the discussion again is just tiring.

https://signal.org/blog/phone-number-privacy-usernames/

Is it possible to use a voip based SMS for registration?

Those are a little easier to get anonymously then physical sim cards.

I believe you can delete your phone number once you're up and running, but yeah that seems like an anti-feature.