We built until two years ago and already thought everything was expensive back then.
When I read here: 1.1 million budget, prefabricated house with 140m² and plastic windows, "you can forget about a carport", "no basement is possible", "own work necessary".
Honestly, I would rather "park" my money in an apartment or a finished semi-detached house and not build at all. If the dream of homeownership ends in a single compromise, I would hold on to it even longer. In 20-25 years, for example, you can sell the apartment and build a bungalow or something like that, the kids will hopefully be out of the house by then.
Considering how much sweat and trouble such new construction causes, I wouldn't take that on for a prefabricated house off the shelf.
In our rental apartment, almost nothing bothered us. I couldn't even say what the door handles or the faucet in the bathroom looked like. It was just an apartment you "temporarily" lived in. In your own house, every detail of OUR dream house that isn't as I imagined bothers me. I would go crazy if I always had to take the cheapest option.
This is just my personal opinion. Maybe a bit condescending when you yourself live in a detached house and write something like this, but with these conditions I wouldn't (anymore) build.