Well, I don't think that there's going to be a way to narrow it down just from that. Can maybe suggest some things to try.

Segfaults happen when an app is trying to write to memory that it shouldn't be. It tends to indicate either a bug (which shouldn't be the case at the application level, given multiple applications doing it), or corrupt memory.

INTEL i7-4790

Well, it's not the recent 13th+14th gen Intel hardware problems; I had two processors produce corrupt memory via that route recently. That's an ten-year-old processor, though.

Memory would be an obvious thing to blame, but memtest not hitting it is an argument against that.

Proton-related stuff -- Windows games running under Steam -- might use a fair bit of memory. Do you have swap space, maybe?

$ grep ^SwapTotal /proc/meminfo 
SwapTotal:        999420 kB
$

I can imagine a swap device corrupting memory. If you're using any swap, I'd probably do a fresh boot, use sudo swapoff -a to disable swap space, and then try your repro case with proton.

It's possible that there's some kind of kernel bug relating to memory allocation that you're tripping, I guess, but you're running an up-to-date Arch, so I assume that you've got a recent kernel, and you're saying that this has been going on for "some time". That would be consistent with problems continuing to happen once the problem occurs on a given boot and a reset making things go away, I suppose.

I guess it could hypothetically be a problem with the Nvidia drivers...if the Proton games you're playing are 3d games, that might be tripping it.

A game might also be stressing the CPU, triggering temperature or other issues. The stress utility would let you generate sustained CPU load on cores (--cpu), maybe see if that reproduces your problem.

Proton games might be loading the GPU...I don't know of a good way to artificially generate load there, unfortunately.

You could try checking the kernel log for any errors preceding the segfaults in the kernel log, maybe when you're running that Proton game; any issues there might give a clue.

The potential common cause points toward the GPU drivers (note of games in Proton, libgtk4 segfaults, and libnvidia-glcore segfaults). What nvidia driver version is in use. A quick search found a rough match to shown symptoms, but is recent and matches the hardware (NVidia Polaris desktop). Perhaps the driver version in use exhibits a similar showing of a regression for such GPUs?

Have you tried reinstalling proton, or installing an older version of proton?

One of a few things is happening

when a game is calling upon proton, and this error is triggered, and your game crashes, it was either because

1. Proton (or some affiliated process) reached out to memory at an address it doesn't have permission to play with.

2. Proton (or some affiliated process) reached out to memory at an address that makes no sense.

3. Some kind of overflow error occured

It was either a misconfig on your par, a new version compatibility issue, or a bug causing something in this stack to reach out to a nonsense memory location or causing a stack or buffer overflow, something like that.

Things I'd try:

Check Protons compatibility with your current kernel version.

Check Proton/steamlogs for more info on what might be going on.

If this problem is new and you recently upgraded... Consider rolling back.