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Pretty sure this was announced at the same time as Sign On with Apple originally, no?

According to the Wayback Machine, the same terms were present as early as October 1st 2019 (maybe earlier; didn't look):

When Sign in with Apple was announced it was stated it wouldn't be a requirement until April 2020.

They also used to say you needed to do this if you "exclusively" used third party sign on. Now it's if you use third party sign on at all.