Reinstall collapse in the ground?

I’m just wondering whether having bricks and concrete in the soil can be problematic...

No one can really help you well from a distance. Maybe a lot of lime was added? Reinforcement in the concrete? Both rather unfavorable in the garden.

Best case would be: they wanted to save money back then and the concrete mostly consists of sand and gravel anyway?

Bricks are not a bad idea in dry, sandy soils, since the clay stores water (like a sponge).

Garage and a bit of driveway sounds to me like after breaking up there will only be a small pile left anyway.

No Haydee, I already panic on my own, no one here helped me with that
I just discussed it with my husband and it came down to the same thing: rubble under the driveway and possibly the terrace. I quite like the idea!