It's supported by polish banks for PLN accounts, but I don't think there's a requirement to be a citizen to open an account. I know Revolut also allows using it, if you create a PLN account in it.

Revolut will only offer BLIK if your address is in Poland, it's not enough to just open a PLN subaccount. Same with Wero, it is only shown for customers in Germany and France IIRC. I have no idea why they did it like that, the backend clearly supports them all.