How to eliminate iMac window transparency/opacity

Is there any way to eliminate window transparency/opacity in MacOS 10.14?

Example: If I move a Quicktime movie around on screen, I can see ghost images of the windows behind it in the video image.

It affects most apps to varying degrees. Finder is least affected in the foreground, and is usually the thing showing thru the window I'm working on. Sometimes the ghost image represents windows that were recently closed. I've put up with it for many years. I've had to reassure clients their expensive artwork does not actually have lines running thru it. It's embarrassing and unprofessional.

Switching on Reduce Transparency in Accessibility doesn't help: it reduces it in the Finder sidebar and Dock.