Who has to restore the height of the garages/parking space?

uhm ... You have already placed the stones and only left out the two pieces for him plus didn’t ask him if he wants to join your construction measure and if you will order the stones for him??

No, L-stones are NOT set yet (in the 1st post: "L-stones also have to go there, ...),
only the garages and the parking space (and the houses) are built/exist.

Behind the garage and parking space is still an excavation pit (work area), now it should be filled up or the L-stone planning begins....
Therefore, I didn’t understand what you meant by "versetzen", you probably mean: "set L-stones" ("versetzen" sounded to me like "relocating" from X to Y)

Please speak in complete sentences:

It's only about the 2m L-blocks that still have to be set ...

So you don't mean that only his two-meter blocks still have to be set, but that all the blocks still have to be set (and that they are 2m high) - the remaining 70 cm are then battered and stabilized with faith in God?
To move (them) means exactly that. The equipment for it is about the size of a tow truck.

OK, sorry, not entirely clear ... By "only" it was meant that only this cost allocation here is still unclear. And the 2m, that is the width of the garage side that needs to be protected. The height of the L-bricks will be 270cm.

Being right... getting your rights... enduring the time until then passes and having to live your whole life with a grumpy neighbor...

I'm no expert, but where is something like this settled? That a parking space is refilled to its original level when you dig it up beforehand?
I'd be interested, because the neighbors around me are also playing funny games with the terrain right now. Maybe I can say then, "Friend... you have to catch that if you think you're going 50cm below my ground here, not me..."

I have no right to see the neighbor's building plans for their property before I start my considerations, do I?

Are there really courts that, if in doubt, meaning if the garage is muddy after 3 years, say "Yes, Mr. B., but that's really your own fault..."?

You have to have L-bricks installed anyway. And if you do it all in one go, the whole heavy stuff only has to be moved once to set the approx. 1.8-ton L-bricks (my car weighs less, even including me... I fear it takes more than 100 butter sandwiches) into place. Can't you agree with the neighbor somehow and share the costs or something?

And about the neighbor blocking off... I always believe in the good in neighbors... maybe he simply doesn't have the money right now? It's happened before that builders are completely broke after moving into the house. Correspondingly tense is then the mood when "wealthier" neighbors ring the doorbell after 2 weeks and want to talk about sharing the fancy designer fence for 25,000 EUR on the shared border in a brotherly way. I don't know your neighbor.
Also, big cars in front of the door are not always a sign of insane wealth, because they might have been bought or leased before the ruinous construction project. You guys are probably the best judges of where your neighbors stand financially, if at all.

And in the end always the advice that rarely comes here, because the forum users do not have to live next to your neighbor.
In doubt, you have this neighbor forever... whether you want to mess things up now... you have to decide ;)

Sorry,
I don’t understand your sentences ...
> "Are there really courts that, in case of doubt, meaning if the garage is muddy after 3 years, say 'Yes Mr. B. But that is really your own fault...'?"
The earth was temporarily removed to be able to build the garages there, now it should/must be filled back in.

> "That a parking space is refilled to its original level if it was excavated before?"
No one is interested in that, then he would have earth on his entire side wall!

> "You have to have L-shaped stones installed anyway."
Correct!
Do you know the price for having 2.70m high L-shaped stones installed?
Four figures per stone (1m wide)

> "Can’t you agree with the neighbor and split the costs somehow or something?"
That is exactly the point!
We (A) of course pay for our 3m stones (each 270cm high), but the 2m on the side of his garage are in my opinion "his business."
Should I be such a nice person and participate (unnecessarily) in his costs?
We want to have it done together, but the question is: Who pays what?

> "Designer fence for 25,000 EUR on the common boundary to share amicably."
What is this "comparison" supposed to be??
Did I ask for or write anything like that?
I just don’t want to be taken advantage of (in other words: disadvantaged), and it looks like that would be the case if I were to pay for his L-shaped stones!

> "In case of doubt, you have this neighbor forever... if you ruin it now already... up to you"
Do we have to know?
Only as information, until today it was clear: we our 3 meters, he his 2 meters.
Then came information that he had spoken to a lawyer and we must not endanger his garage with the filled earth and therefore also have to bear the costs of the necessary L-shaped stones ...

All in all, a "strange" post from you ...

Or am I the only one who can’t make sense of this post?

No, you are not alone. The Lord often tends to exuberantly miss the mark on topics - the side-track mocking is his lifeblood.