What if you routinely want to look at multiple windows? Can you easily choose which windows are not dimmed of the many on your desktop?
You can set it up so the one active window on each monitor is not dimmed, so if you have two or three monitors you can have two or three non-dimmed windows. You can't do anything more fine-grained than that, as far as I know. You can also toggle the dimming on or off with a global hotkey.
Not exactly the same thing, but I have 3 physical monitors in Windows and when I need to go into focus-mode I sometimes use an application called MultiScreenBlank[1] to dim or blank out the screens I do not want to bother me.