Vertical line at center of Mac monitor with Mac mini
I have a newer Mac mini. It has operated well with no problems. On one of the last updates, macOS Mojave, a vertical line appeared down the center of the screen. Bothersome, but it didn't affect operation. It has similar color banding to whatever the desktop picture that is showing. With the last two upgrades [10.14.4 and 10.14.5 ] the line disappeared. I just did a security and Safari upgrade 10.14.6 - and the vertical line is back! It seems this can't be a monitor issue since it directly corresponds to software system changes. I tried restarting with PRAM reset as others suggested, but no change. Any ideas??
Mac mini 2018 or later