Intercepting higher neighboring plots: L-shaped stones, etc. - Tips

What angle should the slope have? There are alternatives to 90 degrees... We prefer natural stone.

For this purpose, there are also L-shaped stones that have the feet on the other side. However, in my experience, they are significantly more expensive than the standard models.

Sounds a bit like a left-handed mug. What is different about these L-shaped stones?

We have the same problem. In a gap between buildings, we want to lower a section of the property about 5-10m long by about 1.5m deeper than the neighboring property. Until now, we were thinking of a natural stone wall, since these planting stones are not exactly the "yellow from the egg". But I still don't know how this is supposed to work. The perhaps dumb question I ask myself is how do you secure the slope during excavation before you secure the slope?

We have the same problem. In a building gap, we want to lower a section of the property about 5-10 meters long by approximately 1.5 meters compared to the neighboring property. So far, we were thinking of a natural stone wall, since those planting stones aren't exactly top quality. But I still don't know how that's supposed to work.
The perhaps silly question I'm asking myself is: how do you secure the slope when excavating, before you actually secure the slope?

Just like you secure an excavation pit.

The perhaps stupid question I ask myself is, how do you secure the slope when digging before you secure the slope?

If there is a building on the boundary, it will be expensive. If not, the neighbor should tolerate the intervention. Very steep slope for a short time. Secure with foil against erosion. Install support element, refill the neighbor’s terrain and restore the neighbor’s property to its original condition.

But I would only tolerate that as a neighbor if you do not have enough space to carry out the entire work on your own property.

Sounds a bit like a left-handed mug. What is different about these L-blocks?

Well, for everyone who is surprised by this and is thinking of left-handed mugs ;) , here is the solution to the puzzle: The exposed concrete on these models is simply on the other side. This means the "nice side" is on my property, without me having to interfere with the neighbor's land. Unfortunately, not all suppliers have these models in their range. I am just attaching the model and price overview of my supplier. This clearly shows the difference (also in price).

Thank you icandoit. They are all detached single-family houses, i.e. at least 3m distance to the boundary. Concrete walls (partly to compensate height differences, partly intended as fence foundations) were already sunk around each property ages ago, but I have no idea how deep they go. There are probably no standard values for this. Therefore, we will probably have to uncover them partially by force. Maybe they can be reused and the slope only retained up to that point. But maybe that would look totally stupid.