Thank you for your answer. Nowhere did I find the info regarding Boot1. I also dont see it in the spec sheet. I might need to look into that.

But long story short. I was stupid. The programmer did nothing with the reset pin even though it was connected correctly. I tried doing it manually many times with a wire. But instead of pulling it down, I've pulled it up 🫣.

So pulling it down to GND manually with a wire did work.