Based on that output, I agree with the other comment that gamescope is your culprit. Try running this:

sudo cat /sys/module/nvidia_drm/parameters/modeset

It was in the last set, but I left off the sudo prefix on accident. If it outputs “N” or “0”, we’ve got an answer: gamescope needs KMS to run, but you’ve got an older GPU driver version (v550) and DRM (which KMS depends on) isn’t turned on by default until v560 per https://wiki.archlinux.org/title/NVIDIA#DRM_kernel_mode_setting.

So if that is the issue, this should sort you out as a fix and get gamescope running again. Be aware that it’ll reboot your PC in the process:

echo 'options nvidia-drm modeset=1' | sudo tee /etc/modprobe.d/nvidia-drm-modeset.conf
sudo update-initramfs -u
sudo reboot

Good job putting this together! Lots of useful info in your post.

My eye is locking onto this bit in the logs: vkCreateDevice failed (VkResult: -7). Vulkan is failing to initialize, seemingly because of some missing extension.

Try these for us and share your output, if you’d be so kind. Feel free to scrub any parts you don’t wanna share with a [REDACTED]. I’m mostly going off memory so some of them may fail and that’s okay:

sudo dmesg | grep -i err | tail -10
nvidia-smi
inxi -Gxx
which vulkaninfo
which amdvlk
which vulkan-intel
vulkaninfo --summary
gamescope -- vkcube
vkcube
cat /sys/module/nvidia_drm/parameters/modeset