Technically, this is possible!
As for any other bank account, you just have to link your American Express card to your Qonto account. Then, transactions made with your AMEX will debit your Qonto account.
But ... your Qonto account works with systematic authorization requests because it cannot be a debtor.
As American Express cards operate at a deferred debit, there may be a risk of loss if your Qonto account does not have the funds at the end of the month to honour the amounts owing.
For this reason, they have chosen to do not accept Qonto accounts 🙏🏻