I'm close to giving up on Witcher 3.

Recently, I got a new CPU, an AMD Ryzen 3900x. Before that, I can't remember having problems with CTDs. I googled and googled and tried all types of solutions. Ran it in admin mode, which didn't help, ran it in borderless window mode (as the support on gog suggests), which made the CTDs even worse, tried deactivating v-sync, tried uninstalling and re-installing, and so on and so on.

My system is:

Ryzen 3900x on an ASUS Board (I think 570-E or something)
64GB RAM 3200Mhz
2tb Corsair PCI-E NVME SSD (the newest one)
2x EVGA 1080ti
Windows 10 Pro (fresh install)

Does Witcher 3 have problems with my components or something?

I don't get any error messages. Sometimes it's just a pure CTD. During discussion scenes the screen freezes and I can still hear the whole discussion, as soon as I alt+tab, the game crashes, though.

I stresstested my CPU, RAM and GPUs and everything is fine. All the other games run well. I don't know what I could try anymore.

Really would like to play the game some more, but I'm losing hope.

I experienced something like that around 2 years ago. Turned out my PSU (power supply unit) was dying on me. It still provided power, but not enough to keep the fans running so the pc stayed cool. I had CTDs and even complete power downs due to it. After replacing it, the problem was fixed.
Not saying that that's your problem, but it wouldn't hurt to check it.

You could try a program like HWiNFO from https://www.hwinfo.com/ or some other diagnostic tool.
It will check temperatures among others.
You might also want to check Windows' device management. Perhaps you can see there if one of your components has issues.