we once had the house placed on the existing plot.
The house should be planned according to the plot, not the other way around - I'm confused? Are you building with an architect? Or with a general contractor?
... unfortunately, the plot has a drop of about 1.5 meters right after the street
Wonderful, why unfortunately? That way you can build something really cool, not some run-of-the-mill house. If you don't want it, why do you have it then?
My wish was actually to have, after the terrace which is supposed to be at the front left corner of the house, a piece of flat garden/lawn to be able to host guests in the ground-level garden as well. The architect says that's hard because outside the terrace the terrain is not allowed to be raised over one meter without approval, which would be necessary.
Why not a balcony/raised terrace?
Furthermore, I don't yet like the solution with the carport supported by retaining walls.
Ditto
The advantage is that you can build a nice basement apartment on top, which is almost a ground floor apartment with a nice side entrance and a small terrace between the house and the carport.
Yes, exactly! You just need an architect who plans the house according to the plot, not first the house and only then looks at the plot....