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

Hello,
we have built and now we have an "uncertainty" about who has to bear the costs for the necessary L-stones in the area of the garages/parking space.

For your information, there are two houses, the driveway area and the house area of both houses were excavated and are now at (let's say) 0 meters height.
That fits.
The area for the two garages and the parking space between the garages is also at 0 meters.

Garage A is (at the back) earth-pressure resistant and is to be filled with soil.
The adjacent parking area A will receive L-stones at the back so that the garden area returns to the height level as indicated in the building plan (let's say: height 270cm).
Neighbor A will pay for these L-stones.
It is unclear what happens with the area marked in red.
L-stones are also needed there because the side wall of garage B is not earth-pressure resistant and must be protected from soil on this side.

Neighbor A argues:
B must pay because the (original) height, as in the development plan (in the garden area), must be restored and in the 2m area of the side wall of the garage soil must also be refilled.

Neighbor B argues:
Neighbor A must pay for the L-stones on his garage side wall (2m) so that no soil can press against and damage his garage side wall.
The refilled soil would damage neighbor B's garage.

How does it look, how are the heights to be understood in the development plan?
Does A have to bear the costs so that this height can be restored,
or B, because the red area must be brought back to the height in the development plan by him?

So you are Neighbor A and you have excavated your property towards the valley-side street by two meters seventy from the hillside original ground level at driveway height and after building the garage, you filled the ground behind your garage and the adjacent parking space back to the original height. Neighbor’s garage is at the same height as your garage / parking space / driveway. At what height is his garden and did it remain untouched, is his garden or yours behind his garage?

You interpreted everything correctly!

At what height is his garden and did it remain untouched, is his garden behind his garage or is it also yours?

His garden is at the same height as ours, like the garage, so 270cm "higher" than the parking space, garage driveway ...
The red line is the boundary, behind his garage is his garden. (also about 270cm higher than the parking space, on a level with the garage roofs)

L-shaped blocks also have to be placed there because the side wall of Garage B is also not earth pressure resistant and this wall must be protected from soil.

I am not an expert, but isn’t the fault already where the neighbor builds a non-earth-pressure-resistant garage directly at the boundary, where, according to the original terrain height, earth pressure is a risk?
He cannot expect or demand that neighbor A places L-shaped blocks along his garage on his property. Regardless of the question of who pays for them?

The earth pressure in the area circled in red on its sidewall was therefore only temporarily missing while you were excavating the terrain, which there has only now been restored?

The earth pressure on the side wall in the red-circled area was therefore only temporarily missing while you excavated the terrain, which has now been restored there, right?

Exactly, it was only removed to set up the garages and the desired parking space, and it was clear that the level behind the parking space would be restored to the original level (using L-shaped stones behind the parking space).
Incidentally, his garage was only installed together with our garage and the parking space! Before that (until 4 months ago) there was "earth" everywhere.