But you can still show your nipples at the non nude section

You can also show your dick in non-nude sections. You have to be sensible of time and place but the likelyhood of someone complaining is very low if you do it near a lake or the sea. Pretty high when you do it in the city center or in church.

At least it was common in the region I lived, there are more prissy places though. I wouldn't do it anymore when everyone has a smartphone though even if taking pictures will get you in huge trouble too.

Sure, but even that has become more uncommon than it used to be, in my experience.

By custom yes. By law, whole Germany is nude section. You have groups of nude people in public parks, right in the middle next to bike road.

Topless, yes, but nude?

Yep, nude.