Walling up the garage (underground garage)

Hello everyone,

We bought a house in November last year. It has an underground garage. However, due to the slope, it cannot be used as such. According to the previous owner, there was never a car parked in it. (Fehlplanung)

I have already asked the building authority. I do not need a permit for it.

I will have the masonry done by a professional.

Can you still tell me in advance how this can be done? So, which bricks? Does it need to be anchored to the existing masonry? (Because of stability)

Later, the wall is supposed to get a black coating and be filled in. Maybe a car should be able to stand on it then.

Thank you very much in advance

When the ramp is filled, under no circumstances should a double-skin masonry with an air cavity be constructed, as the earth pressure could deform the 11.5 cm. I would orient myself to the already existing wall, but at least use 30 cm masonry. It is important to me that the wall has no offset on the inside. Since it will be filled, an offset to the outside is probably not so bad.
I also spontaneously thought that I would shutter and concrete it. Anchoring to the existing masonry is definitely necessary.
On the outside, I would create a 5 cm wide fillet.
If masonry is to be built, sand-lime brick is probably the right choice.

Um, where is my answer?
Did I say something wrong?