No, you are not understanding how it works. Ubuysa explained it very clearly. The CPU is designed to run at 100% (or sometimes more) so it is not "stressed" as you say.
If you are that concerned then limit the number of threads the zip utility uses to less than 24, I suggest you google how to do...
It isn't how much CPU it uses, it's how long it takes that matters. If it used 1 core it might take 12 minutes but using all 12 cores would take 1 minute. Bit simplified but you get the idea.
There seems to be a mix up between VRAM and system RAM in this thread. It is a surprise though that system RAM of 32GB is dropping relative to 16GB. This will have less effect on gaming than VRAM.
As it is a time-based fault there is no way to know until many months have gone by. If you are interested in buying a PC then buy the much superior AMD offerings and forget about Intel.
This one looks reasonably balanced albeit on an older CPU and slightly over budget.
https://www.pcspecialist.co.uk/computers-for-next-day-delivery/1608/
As you are only running 1080p a 4070 would save you £80 compared to the Super, and be more than adequate. It's also much more power efficient so won't tax your PSU as much. This build is pretty much the same as mine and will be 100% good enough for every game at 1080p.
It needs an 8-pin PCIe cable from the power supply. If you can get at one and route it through to the new card then it will work. Note though, as Tony says, 450W may be cutting it fine and you could get system instability when playing demanding games.
The 5800x isn't that much faster than the 5600 and consumes more power so running 24/7 would cost more than the benefit. You have a limited system running AM4 on micro ATX so I think a new build is needed on AM5 with a more powerful CPU and faster memory. Running 24/7 you need to factor in...