Retaining walls at property boundaries. Who is allowed what?

So you have dug, you have to intercept, you pay, you decide. It's that simple, if then a neighbor wants [L Steine], he should put them on his property. Or you talk to each other and agree and share the costs.

That's not what it's about at all. Of course we are intercepting the slope caused by the excavation. The neighbors are also welcome to place their L-bricks in accordance with the development plan. We are only concerned about what happens if their L-bricks really press against our wall and break in the process. And then, in the worst case, we will probably have a gorge of 3 meters. Because permission has already been asked for here, I have to naively ask. Is something like that taken into account in the building permit, meaning whether such constellations can occur? I mean, one person doesn't know what the other intends to do. But the building authority does. I will probably call there tomorrow as well. I thought the whole thing would be a bit easier to clarify. Thanks anyway.

Why should the neighbor lay L stones again, did he pile them up? Explain or what don't I understand? Or just out of fear that your wall won't hold?

Don't you have a picture? How is one supposed to understand it like this?

Until the one point forty that you dug out becomes three meters, your neighbor first has to pile up one point sixty against it. To execute such a guillotine-steep step – since we’re talking about L-stones – in my humble and occasionally fallible opinion can only be done by someone who has never seen a slope slide or is otherwise deeply convinced that mankind’s highest happiness lies in the negation concerning the basics of Fühsick or whatever it’s called. Besides, such hardcore engineering structures are also a matter priced at five stars Superior. I hereby invite to add his two cents.

Don't you have a picture? How are we supposed to understand it like this?

You are right.
Please don't take the proportions in the graphic seriously. It is only meant for clarification.