At about the same time I created this episode, I got a monitor from AOC. You can access the settings menu via 3 physical buttons on the from of the right bezel.  The problem is they are those buttons you can't really feel.  There are labels on them but those labels are hard to feel, too.

This resulted in numerous failed attempts to make needed adjustments.  Frustrated me enough I've used one monitor for the past couple of weeks.

Today I finally got around to solve this problem.  At first I put the monitor on it's back so I could get a good look see.  With good lighting I was able to see the buttons clearly and make the necessary adjustments and  have dual monitors again. Hooray!

In on of the most epic DUH! moments, I thought ot  this episode and added landmarks to those buttons.  So far so good.

Generalization:
If you have something that would benefit from tactile landmarks, superglue might be the answer.