Checking for software vs. hardware keyboard problems.? Lenovo A12 YB-Q501F Android 6.0.1
In this particular case, I discovered a small hairline crack along the physical keyboard section. (It is touch-based and flat, with no physical keys, just outlined sections for key placement.)
Everything on one side of the hairline crack is not working, and most of the stuff on the other side is, with some errors.
Although my device's problems can't be solved through software, @alecxs had some good advice for listing and monitoring devices, if that is useful for however finds this later!