The general consensus in the german legal system is that a dashcam that records on loop is not allowed; you basically film people without their consent and with the intent to distribute to third parties (the police) for no good reason (the possibility of a crash).

On the other hand, what is permitted is dashcams with shock sensors and trigger buttons. The shock sensor gives you a good reason (very high probability of a crash).

Using the trigger button is okay if either there was a crash (or something illegal) or if you mask out any identifiable details about the car and person involved afterwards.

Generally, recording public spaces is illegal, if you setup a security camera on your property, you have to make sure it's not filming outside your property in an unreasonable manner (you may be allowed to film the sidewalk, for instance, if you suspect someone is salting your garden out of revenge, but only until you have proof and then you have to make sure to delete all non-essential footage).

Privacy in public space is an important right that doesn't exist in the US.