Some more details: various people contacted ASN, but they are mostly pointing to Wero. The Play Integrity check is performed in the method nl.devolksbank.mobile.banking.security.data.wero.IntegrityRepository#requestIntegrityToken. From the name, this seems to be ASN's own code and not an SDK from Wero. Someone also found that the integrity token gets sent to ASN's own servers: https://m.devolksbank.nl/bspc-payment-consent-administration... (De Volksbank is the owner of ASN).

If this comes from Wero as they claim, I guess we Europeans in countries that are covered by Wero are in for a bad time. That said, some Dutch banks also made the migration from iDEAL to Wero and don't require Play Integrity.