We had a general contractor who, due to his good reputation, could practically choose his clients freely. His architect was then commissioned for services phase 1 to 4 with a fee in a separate planning contract in advance. After that, he calculated the house construction based on the design and made an offer for turnkey construction. Everything worked perfectly, and we also had the design calculated by other companies for comparison.
Signing the entire contract for turnkey house construction blindly without a design would be complete madness, I completely agree with that.