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
You can also get a phone number in a number of ways without it being connected to your identity. You can use voip services or buy a phone and a SIM in cash. I still think this is a good think to point out for all the people who use signal or other services with a phone number directly connected to their identity.
Depends where you live. I’m in Australia and phone companies aren’t allowed to activate a number without tying it to an ID. So criminals just use stolen IDs and regular people don’t get privacy. Also YMMV but virtually every service that needs phone verification won’t accept VoIP numbers anymore