A plea: bunq's German branch in Cologne should pay German customers' taxes on interest automatically ("tax withholding") like other banks that offer services in Germany. Yes, even though it's a Dutch bank. Triodos N.V., a Dutch bank with a branch in Frankfurt, Germany, offers that service so there's no reason bunq B.V. can't do the same.
Taxes are a hassle and making banking harder for customers than it has to be isn't easy banking.