Hanging works, leveling from when is approval required?

Yes, but I want to be able to walk there, harvest, etc.

What does leveling mean for you? Flattening 50 cm? One meter? Even if writes it differently or corrects me: I do not think that you need a building permit for a raised bed, mounding potatoes, or a buried paddling pool. And you mention something about a 4 sqm and an 8 sqm area. So what exactly do you want to install?

Even if @nordanney writes it differently or corrects me: I don't think you need a building permit for a raised bed, hilling potatoes, or a buried paddling pool.

No, usually you don't need one. But your general statement was not correct. Hence my reference to the respective building regulations – NRW allows you to dig 30sqm however and wherever you want. Other federal states, different rules.

Unfortunately, the OP does not write specifically.

My general statement is not general because ..

But your general statement

as you like.

..refers to..

2x2 M 2 x4 M

...

From when do you need a permit 2x2 m 2x4 m ....?

Check the regulations on site. Country, possibly also municipality/district.
If necessary, you must prevent your earthworks from letting water run onto the neighboring property during rain.

In this regard: Showing some consideration for neighbors helps – they should not be disadvantaged by the level. If that is to be feared, I recommend talking first, then acting.

What are your experiences?

Good. In the course of the house construction, we redistributed the moved soil on the property and thus terraced here and there. That is proving effective. Visually, we made sure that the character of the sloping property remains preserved.

What do I want? Well, simply flat surfaces, it should go in the direction of terraces. In any case, thanks for the hints! Partly this has already been done - a garden shed is already standing on about 6 x 2 m.