How can TOTP 2FA be activated on a Google account without first activating SMS 2FA, and therefore entering a phone number?
You can do this by enabling the "Google prompts" second factor authentication, which doesn't require a phone number. It can then be disabled afterwards.
- Enable the "Google prompts" second factor authentication using by signing into your Google account on Android or iOS (it can be an emulated Android device, as long as Google Play Services are installed and working).
- You can now enable TOTP second factor authentication, for use with Google Authenticator or whatever authenticator you want without a phone number.
- Now you can sign out from that phone to leave you with just TOTP auth. To sign out, it may be necessary to remove the phone from the signed-in devices list in account settings on a PC (it can just be a mobile browser in desktop mode, i.e. using a desktop user agent).
Note: Using FIDO U2F or Passkey authentication may be another option instead of Google prompts, however those seem less straightforward to setup.