Parking spot at the house, fenced on three sides??

What do you actually want: your money back for the parking space, someone to give you width from another parking space, or to swap this parking space for a more convenient one? You won’t find a law with a table appendix demanding a steadily increasing fat surcharge linked to the index of new registrations of Jaguars and Bentleys for every new year a house is built. Bury any hope that your parking space is immoral and that the purchase price would have to be refunded to you. My driver’s license is pink, and despite a fair amount of corpulence, I can still easily get out of a 2.46-meter-wide parking space. By the way, not only from my everyday dinghy, but also from the W124. If I couldn’t do it, I would have someone whose driver’s license is still gray show me how. Or you buy yourself a car with gullwing doors ;-)

There must be a legal regulation or an ordinance, and that is what I am looking for.

You have already found it, the SBauVO. However, if the condominium was approved before 2017, the dimensions you quoted did not apply, but rather 2.30m, 2.40m, and 2.50m. In my opinion, the location of the rainwater downpipe is not part of the scope of the building application inspection, and according to your information, the fence was only recently erected. From a public-law perspective, everything is therefore in order, so a law, ordinance, or statute will not help you.
As already mentioned, the site plan is suboptimal because important information cannot be derived from it, for example, the location of the property boundaries, fences, paths, and driveways, and the meaning of the hatched areas. However, my crystal ball told me that your parking space is not on a property boundary and thus the erection of the fence is purely a private matter. A solution must therefore be found with the builder of the fence.

the rear neighbor has the exhaust gases in his garden

Even if you had a two-stroke engine or a '73 240D, the neighbor would have to tolerate that.

one would have to get out on the side of the fences, that is simply not possible.

o_O

that's not possible at all.
Proposal not feasible.

That sounds a bit stubborn now ;)
"Nothing possible - it's a matter of principle"

well, my parking space is only 220cm wide at the relevant spot. On the left the house wall, on the right another parking space. Parking forward (if the neighboring space is occupied) is out of the question. Backing in is also a challenge if the neighbor once again has used his space right up to the line. I then have to get out into the "flowerbeds". Opening the door fully, as would be nice for my joints that hardly fold due to rheumatism, I can completely forget about. So neither legally approved nor sensible, the building is from 2018. But what can you do, I learn from it and build parking spaces that are almost 3m wide for my tenants and myself! Here, for the OP, ultimately probably one less apartment would have been built if every parking space had corresponded to a respectable size appropriate for the current time. Better either way? And what does the OP want? Cancellation, another parking space, reduction?

Thank you for the constructive and useful information regarding my topic. Unfortunately, some comments are not helpful and verge on the ridiculous, which does not correspond to this professional forum and of which I am disappointed. In other cases, questions remain open and the fault lies with me, possibly because I did not express myself clearly enough. Therefore, to clarify once again:

[*]The car that parks in this spot is a Mercedes A-Class whose side mirrors cannot be folded in.
[*]On the left side of the parking space, the house borders the rear part.
[*]At the front side of the parking space, the property of the lower owner's apartment borders with a fence.
[*]To the right of the parking space, the property of the neighboring house borders with a fence that has a gate.
[*]Both properties/houses belong to the same developer and were planned after 2016 and completed in 2019/2020.
[*]The parking space boundary on the right is therefore also the property boundary.
[*]The parking space is named and assigned in the purchase contract but without size specifications.
[*]The fencing was not mentioned anywhere; otherwise, everything would be fine.
[*]The fencing was only installed recently.
[*]It is clear that the passenger must get out first and this is not a problem.
[*]The driver’s door only opens so far because of the rainwater pipe and the house wall that exiting is not possible if the vehicle is driven all the way to the front end of the parking space and to the right against the fence.

For me, this represents

[*]A clear planning error by the developer.
[*]Legally, this cannot, at least so far, be proven, which is why a regulation is being sought here to prove it.
[*]Then a practical solution is sought, which, for example, could consist of the parking space only being driven to the house wall and the driver then having to get out via the flower beds at the front of the house.

I hope I have contributed to objectivity and look forward to numerous comments. Many thanks.

Whoever is looking for "die kleinste Garage der Welt" will find something funny. Sorry, I can't contribute anything meaningful. But at least something funny. :D