Outdoor area, slope towards the neighbor, how to frame?

Maybe a mixture is the right choice for you. Fence, where slow-growing trees, perennials, hedges, etc. are planted, trellis for roses, clematis, fruit, raised beds

This is a public playground.
Lowering the wall to the neighbor was the idea, so that the balls don’t always roll down. But of course, that's only true for a few years as well.

Honestly, I wouldn’t build a wall right on the edge. It’s purely a gut feeling. The wall presses, edges are usually less compacted and don’t really hold if something is supposed to slide. Roots keep the soil where it should be.

I would put a fence with a door around the public playground.

I think something like that is really the best, you're right. I also don't like the idea of having a wall at the edge at all. I'd rather plant everything green and create a natural boundary with hedges/trees. We really like the neighbors downstairs too, and if there's a wall, it feels like a kind of "isolation" to me.

The side facing the playground with a fence, that's a good idea.

I currently have a similar planning challenge, although not quite as steep. Maybe this fits in quite well here.

We are currently in the construction phase, and due to the backwater level, our house was raised a bit. During the excavation work, our terrain "grew" a little, and after the house construction is completed, it might also be conceivable to add some fill here and there to level out the hilly landscape. We’ll see. Now we are above the neighbor.

As of now, a small "slope" has formed toward the neighbor’s garage and property. Without measuring, I estimate about 60 cm. I am not very interested in elaborate, costly L-stone constructions. Also because this problem extends about 20 meters long, sometimes more, sometimes less intensively.

Do you have any ideas? I had thought about planting ground covers like star moss or bear’s foot grass if that would be sufficient for stabilization. I have zero experience with whether something like that would suffice.