Is the PC dust free. I ask because you say it was never opened to be cleaned.
If it's dusty I would clean all that out and try reseating the GPU. There have been times where debris got into the PCIE slot somehow and the components weren't making proper contact, causing issues like this.
If you are on Windows I would do the following. I'm not familiar with the OS you listed at all so I have no input in the case you are using that.
If it's clean and properly seated I would boot to safe mode and use a program called DDU to completely uninstall GPU drivers and restart and install current drivers.
Provided the problem is still there I would try other ways like command prompt in admin and run "sfc /scannow", and if that doesn't fix it I would restart, open command prompt in admin again and I would run "DISM /Online /Cleanup-Image /CheckHealth", then "DISM /Online /Cleanup-Image /ScanHealth", "DISM /Online /Cleanup-Image /RestoreHealth"
In the event none of that works, I would try the GPU in another system and see if there is artifacting in that system. If it is you have something wrong with your card.
Good luck.
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