Nowadays, a majority of apps require you to sign up with your email or even worse your phone number. If you have a phone number attached to your name, meaning you went to a cell service/phone provider, and you gave them your ID, then no matter what app you use, no matter how private it says it is, it is not private. There is NO exception to this. Your identity is instantly tied to that account.
Signal is not private. I recommend Simplex or another peer to peer onion messaging app. They don’t require email or phone number. So as long as you protect your IP you are anonymous
Signal allows you to speak confidentially, therefore it is private. It is not, by default, anonymous. Yes, this plus the centralized server mean that potentially dangerous metadata, like relationship maps, can be collected. All indications are this isn’t the case, but that’s not something you can count on.
If you need anonymity, which you probably do at least a bit, use simplex. And yes, having more people using anonymous services like simplex is a good thing for the community as a whole. That said, I’m not going to try to convince all of my friends to use simplex. It’s just too far from the mainstream, missing too many features. Signal is a sufficient compromise for most people, and it’s sufficient for me for most purposes.