Screen washed out with bright green or other colors, often flickering

One day my G020 Pixel 3a’s screen starting coming on with a bright, solid green, brown, or tan color behind its displayed image, as if every green & red pixel were stuck partially on, making it washed out & very hard to read. Occasionally it turns a more pinkish color. The spurious background lighting is usually solid, but sometimes flickers in and out, with flashing horizontal lines (in portrait orientation). Once in a while the issue goes away on its own, and the screen is perfectly normal until it’s next turned off (manually or via timeout, even for just a second) and back on, after which the washed-out color inevitably returns.

When enabled, the dimly-lit AOD with clock & notifications is never affected, always showing a solid black background as it should. The spurious background is present from initial power-up (Google logo) onward, even after entering the bootloader, which would seem to rule out a software issue. Rebooting doesn’t help, but repeatedly turning the screen off & back on via power button sometimes eventually clears it for a while.

The spurious color’s intensity goes up & down when adjusting screen brightness, but is always present even at minimum brightness on a black screen (except for the AOD somehow not being affected).

This problem didn’t coincide with a drop or other physical shock, but I originally bought the phone from eBay, so its previous owner might have been rough with it. It was being carried in the tight side compartment of a faux-leather purpose, though, which might have imparted some bending force. Trying to bend, twist, and push on various parts of the screen and case has no obvious effect.

Is there much chance that this is merely a loose screen cable, easily fixed if I can get the phone open? Or am I looking at a replacement screen? Has anyone seen a problem like this before, on any AMOLED display?

Thanks in advance for any insights!