PC sometimes randomly completely freezes, forcing me to restart by holding down the power button.

Extra details:

• Mouse does not move
• Sound "freezes", playing a monotone sound that I now sometimes hear in my nightmares
• It (usually) happens when the user is under high load. But the definition of "high load" seems to decrease by the week.
• Temperatures when using coreTemp seem somewhat fine, in the 70 - 90 range
• My PC is 8 years old soon, but it works completely fine except for this one issue. So if I can fix it, I'd want that instead
• CPU and GPU also doesn't seem to be the issue. At least, if it is, it has to be a very quick and large spike. I can usually play games using 99% of both CPU and GPU, with "no issues" except for, well, this issue happening sometimes.
• It once happened while I was away from my PC, no expending many resources, making me believe it's not about the CPU/GPU
• It happens usually after around an hour or so. But can take much longer, or sometimes only 30 minutes. I seems to become more common the more it happens during the day, which was why I thought it may be temperature related.
• I added more thermal paste about 8 months ago. Perhaps I need to add more again?
• I've tried updating drivers, everything seems up-to-date according to Windows.

Hardware:

• GTX 1080 Ti

• i7 8086k

• TUF Z370-PLUS GAMING

• Installed physical memory: 31.9GB

• Available physical memory: 20.7GB (Is this weird?)

• Total Virtual Memory: 33.9GB

• Available Virtual Memory: 19.4GB

There seem to be very few people online with this issue, but the one single reddit post I found, nobody had an answer. So I'm trying my luck here, 4 years after that post