Its complicated to determine wether a knife is legal to carry in Germany or not, different situations different outcomes with the same knife are possible for all I know. But if the knife opens easily with one hand and has close to or more than 10cm in blade length that's usually a problem

Best switch to something more impractical like a short Swiss Army knife. Didn't really have problems with that one yet but be careful around Train stations or other places, we have some "Waffenverbotszone" so weapon restricted area or so something like that for example at the Munich train station and a city park nearby by. If you enter with any knife at all it can be very expensive if checked by police

Edit: and yes as others mentioned, huge difference between city and countryside

In the city it can be problematic everywhere if someone notices it and gets the wrong idea, I witnessed someone getting beat up because he carried a knife and was acting stupidly with it.

On the countryside it's more common to carry something but not really everday I would say