Hey Koos, it's in fact quite hard to say where you might run into offline terminals. On board airplanes for example are indeed usually offline. Therefore, if a debit card is accepted in an in flight terminal, then so will your bunq Mastercard Debit 💪
In places where only a credit card is accepted, the bunq Mastercard Debit will still not work, as this is a debit card and the acceptance is at the discretion of the merchant.