For me it’s Whatsapp. Like 99% of people i know use it so yeh… i still need it. I am considering moving the Whatsapp Gdrive backup to a local backup btw.
Google photos is also a major problem for us. We have a lot of stuff that want to migrate to different service (or store locally).
Sometimes it’s impossible too. I had some badly designed services where it’s just completely impossible to change email, even with contacting their support team. Email forwarding rules are really good here, but they get confused if you reply with a different email address than they sent to
My vet and my doctors office are like this. Everything for my doctors office says my new email everywhere. Even in the 2FA section. Need to log in with 2FA? Straight to the gmail! No option for an authenticator app either.