Have you tried a fresh install of windows on the nvme with the GPU installed on the system? That would be my next step. Also worth trying a different power supply if you have one. Originally I used a 135w one that would case the machine to shutdown on GPU load, swapped it for another exactly the same and it worked fine.
No particular bios setting other than changing the default graphics option to PEG from what I can recall.
Shouldn't matter what CPU you have either since all the 8th and 9th gen CPU's support the same amount of PCIE lanes.
Thanks again for the suggestions! I tried creating a bootable USB with both Windows and Ubuntu, but when I select the USB drive to boot from, the system freezes right at the start. This happens only when the GPU is installed.
Interestingly, there are no issues when I’m in the BIOS—I can navigate through the settings without any problems. But as soon as I try to boot into an OS (either from the NVMe SSD or a bootable USB), it gets stuck.
As for the power supply, I’ve tested the system with a SATA SSD instead of the NVMe, and it works perfectly fine, even under load while playing games. So power draw doesn’t seem to be the problem. but anyhow I’ll try a different power supply if I can get my hands on one.