About 2 months ago and after about 30 hrs of playtime without any problems my PC started to shut down while playing the game, sometimes it could be after 15 or 20 minutes, but sometimes it shuts down after 5 minutes in the game, no error message or anything it just shuts down, and it has only happened to me while playing this game, I checked the temperatures while playing and the GPU is about 80 - 86 C, while playing other games I've reached the 90 C and presented no problems, I have a MSI GS76 with an RTX 3080, 32 RAM and INNTEL i7 11th Gen.
Is someone else presenting this problem, or has someone found any solution?

90c is way too hot even in other stuff. Generally, 70c is the point between full-load heat and dangerously hot. Most hardware should also be automatically underclocking to reduce heat when they exceed some limit. Finally, your computer shutting down by itself when heat is critically high is by design, to try and prevent hardware damage.

The solution here is to improve your computer's cooling. When it's shut down, open it up and check for and clear any dust buildup with electronic duster as a starting point. If it's a laptop, those always run on the hot side, especially something high-end (but this is beyond that). If it's a desktop, those generally run cooler, but either way there should be general 'my computer is overheating, what do I do?' guides you could look for on youtube or wherever specific advice.

May be tied to a Unity engine-level bug that overheats the CPU for no apparent reason if the game is rendered in fullscreen instead of (borderless) windowed mode. May sound stupid but given the engine's lack of polish, it's worth a try.

This was already reported for Pathfinder Kingmaker: https://forum.owlcat.games/t/game-eating-up-gpu-overheat-to-crash/16392

It is a Unity engine issue, but not a bug-- a nonsensical default function value. The function in quesiton is called, "FixedUpdate". This function is tied to the physics engine, and has to run at a constant rate in order for physics operations to work properly. The (standard platform) default is "-1", which tells Unity to run it as fast as the underlying hardware is capable of. This is unnecessary, and is akin to running a benchmark on your PC for hours on end. It could be resolved if Owlcat would allow us to change the value via a settings option. Additionally, while I understand the value must never be less than the value for the "Update" function (which is Unity's output framerate), there must be a way to allow FixedUpdate to be adjustable and still have a sanity check in place so that it is never eclipsed by Update.

This information is available in Unity's online documentation. It is even noted that FixedUpdate has different default values by platform, specifically citing power draw and heat generation as reasons for doing so.