So, we may have solved the problem....
after countless stupid shit we did.

I've opened her case, took the gpu out, cleaned it as best as I could, and put it back.

Also, while I was cleaning it, I've noticed the "SC" on the sticker. It stands for SuperClocked. So, it has a factory overclock. I started to search the internet to see if factory OC'd gpus are wont to misbehave. And the answer is "perhaps".

So I researched a bit more (about underclocking) and found an option on nvidia control panel, called debug mode, in which it returns the gpu clock to stock factory clocks.

Booted it up, dx 11, did some stuff that would otherwise crash the game, and it looks and feels fine.

Was it the cleaning? The removing and putting it back? The debug mode?

We dont know. Maybe it wanted to be hold in my hands a bit.

Hoping it stays this way.
Thank you kindly, everyone that helped <3