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
2FA is an important security layer, if the service, after sending you the activating SMS with the code, delete your number (normal in serious services), it’s also not an privacy problem. In big us corporations on the other hand, it is, eg.Google store tour number and also probably share it, there 2FA is not an option. Instead a number, some services also admit alternatively a second e-mail account to receive the activation code, there, if you have doubt, you can use an disposable mail, so there isn’t any privacy problem.
2FA helps with security concerns, not privacy concerns. They still would have your number. Also about Google, they have one of the widest spread and utilized 2FA authentication applications out there.
2FA is important, but if you use your phone number for anything, you have no idea how long they retain it, how they directly use it, if they sell it, etc. A real phone number can be mapped back to you trivially.
It should be standard to offer TOTP codes that can be used via an authenticator app, hardware key, etc. Aome places do, many do not.
But at the end of the day, they typically don’t ask for your phone number because they want to give you security, but rather as a proxy to ensure you have a unique identity. Most people will have only one phone number, and it will be more difficult / costly to get additional ones than burner emails, etc.
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.