This means that the phone number requirement has already created a leak of private information

What information? The gov already had the phone number. They needed it to make the request.

Additionally, that was posted in 2021.

Here’s a more recent one.. Matter of fact, here’s a full list of all of them. Notice the lack of any usernames provided.

Also note that a bunch of the numbers they requested weren’t even registered with Signal, so the gov didn’t even know if they were using the app and were just throwing shit at the wall and seeing what sticks.

You are required to provide all information tied to the following usernames

They can’t respond to requests for usernames because they don’t know any of them. From Signal: “Once again, Signal doesn’t have access to your messages; your calls; your chat list; your files and attachments; your stories; your groups; your contacts; your stickers; your profile name or avatar; your reactions; or even the animated GIFs you search for – and it’s impossible to turn over any data that we never had access to in the first place.”

What else ya got?

but that doesn’t help if they get proof in any other way.

If they’re getting evidence outside of Signal, that’s outside the scope of this discussion.

because of the phone number requirement, anything you ever send on Signal can easily be tied back to you should it get out

…no. It can’t.

that subpoena alone is proof that it does.

It’s proof that it doesn’t.