I feel like you're assuming germany functions exactly like the US here.

Every time the police shows up in the documentary it's because whoever the kid photographed insists on having them called as he insists there's no need, but is happy to oblige. Parking Violations don't even fall into the jurisdiction of the cop-cops in germany, that's handled by a municipal department - the actual cops aren't gonna show up for this shit unless you park your car sideways on a main road and then that's because that's not a minor infraction anymore. Everyone in the video would otherwise - maybe - if the municipal department decides to follow through on the cases - get a letter with a fine that they can either appeal or pay and that's a big maybe, they don't usually do anything about any parking violations anyways.

Do the not-cops tasked with minor infractions still suck a lot for related reasons to the cop-cops? Yeah, sure, probably still a lot of racial profiling in there and such, but they're not armed because that's not their job. At most they have some self-defense training in case somebody starts to assault them, usually for writing them a ticket for parking like shit, as that happens a lot. The only way you can get arrested for parking violations in germany is to rack up a huge amount and then refuse to pay any of them despite having the means to, if you show proof you can't pay them they'll just get rain checked until you can.