How do I completely remove transparency on my iMac running macOS 12.7.6?

Just want to completely turn off the transparency of windows. Not reduce it. Completely turn it off. Disable it. I do not want to see my desktop through another window. If that window has a black background, it should only be black. Nothing underneath...

The "reduce" under the Accessibility syst pref does exactly what it says. It only REDUCES it. Can't tweak contrast enough.

iMac (Retina 5K, 27-inch, Late 2015)

Monterey 12.7.6

Thx,

Peace

[Re-Titled by Moderator]

Original Title: remove turn off completely transparency mac os12.7.6