Thanks for the tip, though they're two different systems: the credit score thing blocks a credit card which blocks various online and offline (mainly international) payments; the IBAN is more used for domestic payments and I expect Hungarian will be as often accepted as my Dutch IBAN. Maybe even less because NL presumably has less fraud and is geographically closer (NL is 15 minutes driving from where I live, which makes it even more mind-blowing that their regular bank cards are not accepted here).

I've got a credit card in the meantime via my partner who is German, but that means that the money on it isn't only mine so I avoid using it for things that aren't shared expenses in the first place.