MasterCard refers to DCC as "POI Currency Conversion". Section 3.8 of the MasterCard Transaction Processing Rules (PDF page 90: https://www.mastercard.us/content/dam/mccom/global/documents/transaction-processing-rules.pdf) addresses this:
"POI currency conversion must not be offered on a Contactless Transaction that is equal to or less than the applicable CVM limit"
If you enable Apple Pay or Google Pay, the transaction is processed using the Consumer Device Cardholder Verification Method, or CDCVM. Since CDCVM transactions have an infinite limit (in other words, no matter how large the transaction amount, a PIN is never required for Apple Pay or Google Pay), this means that DCC is forbidden on transactions using Apple Pay or Google Pay.
I have encountered exactly one large chain in Spain which prohibits Apple Pay with non-Spanish cards specifically because they want to offer DCC, so instead they break the payment flow and make you use a plastic card (for which DCC is not prohibited). Dirty trick. They no longer get my business (and I reported them to the Bank of Spain, MasterCard Europe, Visa Europe, and the European Commission).