AI denoise GPU vs CPU time issues

This is a big problem, and it is your GPU as you said, it's overheating. What has likely happened is that your thermal pad inside the GPU has evaporated. So you've got no coolant. You need to get the thermal pad replaced, check the memory isn't fried and remove any build up of dust. Take it to a service agent.

Foregive me if you've seen this solution posted multiple times, but there are so many posts on this subject, I thought it might help if I did so inorder for it to be more easily found. Just trying to help. Sorry.

Your GPU only has 3gb, not 11 (ideally you want at least 8gb), and is otherwise pretty underspecced:

(https://www.techpowerup.com/gpu-specs/quadro-k4000.c1841)

My AMD RX 580 is by no means a particularly impressive GPU, but it takes c. 45 seconds for a Canon R5 file.

Look at the difference in specs. Even if you aren't "a computer guy", more is better - especially around RAM and cores - where Lr is concerned:

(https://www.techpowerup.com/gpu-specs/radeon-rx-580.c2938)

You may want to look at https://helpx.adobe.com/lightroom-cc/kb/lightroom-gpu-faq.html#sys-req-gpu-image-processing 

I can see that happening if the GPU is not supported for Lightroom Classic/Camera Raw graphics acceleration. If the GPU can’t be used, it would have to push all the work to the CPU, overwhelming it. I looked up the release date of the Nvidia Quadro K4000 GPU, and it looks like it was released a decade ago. The CPU release date appears to be 11 years ago.

I’ll have to leave it to the more expert PC users to advise on putting a newer GPU on that motherboard, but given the age, yes, it’s likely that for it to be worth doing that, other motherboard components would also need to be updated to keep the entire system balanced and not bottleneck a current high performance GPU.

As an example (although they’re Macs), I have a 4-core Core i5 from 2018, and it denoises 60 megapixels in three minutes. On a 2021 Mac with an Apple Silicon processor, it’s just over a minute per 60MP image. The graphics hardware in the latest high end PCs and Macs do AI Denoise in under 20 seconds per image.

AI Denoise is one of those features where we have it only now because before about 3 years ago, the hardware to do it fast was not yet widely available. So almost everything more than a few years old is terrible at AI Denoise.