To deal with some of the changes in Mac OS X, I ran apps and system extensions that restored some behaviors from classic Mac OS. Over the years, I weaned myself off most of these, but a few stuck. In particular, I found I did not want to live without the window layering policy from classic Mac OS.
In classic, when you click on a window that belongs to an application that’s not currently active, all the windows that belong to that application come to the front. In Mac OS X (and macOS), only the window that you clicked comes to the front.
My particular style of window management leans heavily on the classic behavior. I also appreciate the Mac OS X behavior in certain circumstances, so I was delighted to find apps that enable both behaviors, using shift-click to override the default.
He goes on to write that the third-party apps he had been relying on to restore this functionally died in the great 32-bit Death Wave of Catalina, so he has re-written a Mac utility named Front and Center:
Front and Center lets you control the window layering policy on your Mac. In “Classic” mode, clicking on a window brings all the windows in that app to the front, just like it did in classic Mac OS. In “Modern” mode, only the clicked window comes to the front. In either mode, Shift-click on a window to get the opposite of the chosen behavior.
Front and Center can be found on the Mac App Store for $2.99, and has a very good app icon: