Is a pedestrian crossing necessary if there is no sidewalk (in Berlin)?

Yes, that is also Plan A.

What worries me now is that in five years or so, when the road construction authority has cleared its backlog, there will be only superficial inspections (drive-by) and then I have to prove that a specialist company carried it out, or rather the file will show that the driveway was never applied for, let alone approved, and then heavy fines will pour down and it still has to be implemented at a cost....

Maybe someone has already had experience with that.

Hmm. I can't find a definition for "nicht befahrbarer Straßenbestandteil". On the Berlin service pages, sidewalks and green strips are mentioned as examples in one place. Maybe that's an approach. It is not a sidewalk, and whether it is a green strip can at least be doubted. Although probably the position of the road construction office will be that whatever is under the crown of a tree is a green area. hmm.

You could also call anonymously or under a pseudonym and demand information :D

uh yes, I have to check again how I can hide my phone number...

If I had meant "wake the sleeping dogs with a suppressed number or call yourself H.K.", then I would have written it exactly like that. Besides, I just flipped back in your quote of the regulation, and it does not even require a fastening. Furthermore, with an indefinite regulation, I see the burden of proof of your violation lies with the plaintiff, and this is not a walk in the park.

Yes, sorry that is stated in the following paragraphs that are not quoted. I'll wait for the conversation tomorrow with the guy from Zeiten and my neighbor, and then we will have to lay our cards on the table...