It depends on how you exchange them.

Until 31 May 2025, you can pay with the banknotes that will become invalid in shops or deposit them in your bank account. After this date, you can only exchange the notes at one of Danmarks Nationalbank's three banknote exchange points. The deadline for using the banknote exchange points is 31 May 2026. Read more at www.forexvaluta.dk/invalid-banknotes