According to several posts made on the Apple Support Forums, some users are claiming that their iMacs are displaying screen glitches where a line just appears on the screen at random. One user writes, “I’ve just received my new iMac and noticed that from time to time a line glitch appears on my screen. It’s completely random, I thought it was related to intensive work/heat but sometimes even when the computer is idle I see the line on the screen.”
Another adds, “Same problem with my iMac 2020, already appeared during the initial Mac setup and keeps flashing randomly since then. Searching through YouTube and google it seems this is a common problem with the 5700XT gpu that comes with it.” Right now, the issues seems to be isolated to iMacs that are configured with the 5700XT with 16GB of VRAM, so the other models should be “safe”.
It is unclear why this is happening and if it is a software or hardware issue, but hopefully a solution to the problem will arrive soon.