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).
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.