Which ones? I never came across any. They may require a "Personalausweis" (like banks) but not a passport (which is a different thing). An EU citizen can come well by without ever needing one, as he can travel the EU by personal id alone. I only need a passport for international travel.
And that makes sense. You can be denied a passport, but not a personal id.
I have definitely experienced the case multiple times online where I have been denied something without a German Personalausweis or a passport. In my case, as a UK citizen I don't have a national ID card, so Passport must do, but the option is never "generic ID card" vs passport, but instead the German Personalausweis. Schufa is guilty of this, and iirc so is ImmoScout.
Well, the only document internationally recognized are passports. Not every country has identity cards like the german Personalausweis, let alone there being an international standard for them like there are for the passports.
The passport is simply the international baseline.
Nobody would complain if they demanded a a recognized identity document (like you need to identify yourself to state representatives). There is no good reason for Schufa to demand stricter documents than the state.
