Does nationality discrimination within EU
Does not accept Portuguese citizen card for identity verification.
Just ridiculous...
N26 should learn a bit more about the maning of the European Union and should not discriminate people based on their national citizen cards, especially within European Union citizens who live in Germany...

Update:
N26: As per your answer, I wonder which "strict" german or EU regulation tells you to ignore an EU National citizen Identity document for a citizen authentication... 
You are deliberately doing citizenship discrimination in Germany and that's unacceptable. Outside of the EU I'm happy to use my passport. but inside the EU for sure it will not be some stupid N26 manager that will force me to use it... 
Stay with your "strict" BS and wait until you get fined or sued... For sure the manager who took that business decision will not be there any longer by that time...