"most websites" has not been my experience at all. Sure, for the big ones like email that's and a lot of dev tooling that's the case. But there's a huge amount of services that requires SMS verification and once you loose access to that number you get locked out. A very common case is loosing ones phone (or having it stolen), at which point you have to log into your accounts again from another device but also don't have access to your SIM anymore.

Funnily Google suite does not offer TOTP with Google authenticator… Unless you use SMS/Voice 2FA first… and then you can activate TOTP, I asked if I can then remove the phone number later, and was told that it is possible, and that they won’t use this number for anything in the future. But who knows…

The NHS requires SMS 2FA - can't get around that.