Bring all windows of active application to top

You can assign a keyboard shortcut to the "Bring All to Front" menu item from System Preferences:

The activate AppleScript command also raises all windows:

activate application (path to frontmost application as text)

If you are assigning keyboard shortcuts to opening applications, you can use scripts like this:

tell application "TextEdit"
    reopen
    activate
end tell

reopen opens a new default window if there are no open "default" windows, like a text editor window in TextEdit. If all default windows are minimized, reopen unminimizes one of them.

It is also possible to use AppleScript to click the "Bring All to Front" menu item:

tell application "System Events" to tell (process 1 where frontmost is true)
    click menu item "Bring All to Front" of menu 1 of menu bar item "Window" of menu bar 1
end tell

I use ⌘ Command~ to cycle windows of currently selected application.

MacOS Mojave.

Brining all of an app's windows to the front when clicking a single background window was a behavior of "classic" Mac OS:

http://hypercritical.co/2020/01/08/front-and-center

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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 click 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.

Sadly, macOS Catalina’s lack of support for 32-bit apps finally killed the last of the apps that implemented this feature. I was alone in a cold, barren world where I had to click on a Dock icon to switch to an app and bring all its windows to the front.

Siracusa released a 64-bit app, Front and Center, to bring the "classic" behavior to modern versions of macOS that dropped 32-bit support.

https://apps.apple.com/us/app/front-and-center/id1493996622?ls=1&mt=12

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.