Ground slab on a gentle slope for a single-family house with a basement

Experienced builders are neither architects/thermal insulation verifiers nor structural engineers. For me, this whole thing is good for nothing but a waste of time. I do not understand the purpose of this "brainstorming"... construction is far too individual for that.

Base slab, thickness, foundation is determined by the structural engineer.
Insulation is determined by the thermal protection certificate.

Compaction of topsoil is not suitable.
For filling, mineral mixture 0/32, possibly the bottom layer 0/45 as well. Compacted in layers, better one time more than too little. If you want to be on the safe side, have the compaction tested by plate load tests.

Everything you fill must somehow be secured. This is done with the outdoor area through green space, terrace, wall, etc.

Anyone who only wants to explain jokes and stupid stuff should rather keep silent.

Who made jokes here?

Sorry, this is clearly out of line in tone (and beyond that in spelling).

No one here can give you well-founded information about that. Anyone who would do so would do you a disservice. This is no place for brainstorming; there are rules and necessities to be observed here.
And nothing else.

what some people want to make up for themselves here is really unbelievable?!

A question about experience was asked.
There are no stupid questions, only stupid answers!

I initially answered it via PM because the question was first in a foreign thread that I did not want to "hijack." So here it is again "to be read publicly":

Can the compacted gravel eventually give way so that the ground/gravel under the house "floats away"?

You can only compact in the sense that something is "saturated" with regard to pressure from above; assuming it cannot move sideways anymore. A substrate not bound to anything sideways cannot be stably compacted. Piling layers on an inclined base is out of the question; you will have to "step" them.

Who made jokes here?

From the perspective of the first responders, probably initially the OP themself. Of course, it is an amusing idea to use a wedge cushion – on which the house would certainly slide – as a "foundation." But the idea is probably just due to an underdeveloped spatial imagination and should not primarily poke fun at the readers.

Since very few people here dig or plan their foundation themselves, but leave it to a professional, the experience is rather limited – also considering the fact that experience usually needs to be gathered in multiples, meaning a comparison should take place. The first page already said it correctly: soil survey by a geologist, combined with the expertise of a structural engineer... that is the successful way.