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
Yes, iy’s always to use with a grain of salt. As said, it ads a security layer, but can be an privacy hole, despte that mail directions are easier to track as phone numbers, at least in the EU, you can’t be mapped back to an user, this is only possible in crime investigations by the police with an court order. Mail adresses on the other hand are unique identifiers which are way easier th track, except you use an disposable mail or alias. Anyway, eg.in Vivaldi 2FA is safe and apart optional, as also the account itself, only needed when you want to use sync or the use of Vivaldimail, blog and other services it offers. In much other services it’s also only an option.