* https://signal.miraheze.org/wiki/Signal.me_URLs
* https://signal.miraheze.org/wiki/Usernames#Username_links
Signal.me links are just a way to easily send either a phone number or user name to someone else. No cryptographic identity. No protection of the phone number or user name. So to get around the ban a Signal user could simply send their phone number or user name over Twitter/X.
It seems that the encrypted username form does provide some identity protection in that it can be cancelled, but for as long as it is active it appears that someone can just ask the Signal server what the associated user name is.
The people involved probably should not be using Twitter/X for this sort of thing in the first place. Mastodon comes to mind as an alternative, but really, anything else.