130f is barely over idle, lmao. if your computer is rebooting, it's probably the CPU or Power Supply, not the GPU. Typically if a GPU has a thermal issue, it crashes the Nvidia driver. CPU and PSU are much more common to spontaneously reboot the PC.

It is possible your PSU can no longer support your GPU (Power Supplies lose capacity over time, and if you were threshold already, it may be tripping like OCP or something)

To me it sounds like if your GPU is outdated, and youve had it for 5+ years, eventually the thermal paste dries out. maybe apply some of dat. take it apart, apply, put back together let it is. watch videos on youtube on how to do it first. if you fail, need new gpu. But you might need a new one regardless. LOL just saying. Valheim is really CPU intensive not so much GPU.

nope no probs im running 1080 and its fine..100% vanilla 100 % GPU for the Game via nvidia control panel

only if the gpu has poor or broken cooling

130f is 55c, thats cold yet
worry at 90+c when its throttling