The Deutsche Post '#PORTO' method does not apply to international shipments, unfortunately. However, you can still purchase barcode labels online for printing, and conventional stamps are simply values in Euro cents so can be used for both domestic and international deliveries.

In addition, the 14-day limit no longer applies. Deutsche Post were challenged in court, and the digital stamps must now last for as long as conventional stamps do:

https://nrwe.justiz.nrw.de/olgs/koeln/j2023/3_U_148_22_Urtei...