I was wondering if this is just an issue with Mullvad or if YouTube is now against VPNs in general.
You can make a Google account without providing phone or email, too. You just need to setup a temporary WebAuthN device (like a virtual one in Chrome DevTools) to unlock the option to use a TOTP for 2FA (otherwise there is a UX dark pattern that implies you need to give a phone number before you can use TOTP).