I don't think it's the video adapter, as I ordered this computer built brand new from a shop I trust last April. I've been using this monitor since about 2011, and I bought it at our local Wal-Mart, where the quality is almost guaranteed to fall short of expectations...

1. Try images in full screen:
full blue
full green
full red
(it's RGB right?)
then try full black
and
full white
easy to make in GIMP and display in Geequie.

Usually, a vertical line (or few) means the HID converter powering the backlights is shot-through (or about to be), I had an laptop (Thinkpad) dyeing on me for a decade (red line 1 pixel @~65% towards right edge)) (!), and the hinge failed prior to the converter in the end!

But if the screen is LED, or the line is horizontal, that would be the VGA fatigue?

Also, VGA RAM tends to change the "muster" over time due to heat-up on load change?

HTH

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It may be worth booting into a live install of something like Xubuntu to add nore weight to the hardware theory. Even better if somebody has a phone with an HDMi converter you can use or something like a Chromecast or Firestick.