> Also, why do you assume that such product would need to be used worldwide all of a sudden

Because I'm talking about not running on any American services. Which Americans can do and do all the time. I don't see how we can reach a point where we can one day not include google/apple sign in and not lose a massive number of potential users. Sure it's possible that one day we'll see a "Sign in with EU login" but below it they're always be sign in with google/apple, for a very long time.

That post mostly concerned infrastructure, you won't likely run the same managed DB with 2 different providers, for example, but you can well offer sign-in with EU/non-EU options, and as long as the first one is viable, I'd say that would already be a win in terms of OP's goals.