I was curious about whether there might be a built-in Windows function to do that, so did a little googling then testing.
For Windows 10, the answer is, “sort of”. If you shift-right-click on the Cubase Windows group on the Task Bar, there is a Minimize All Windows entry in the pop-up. I say, “sort of,” because, when I tried this just now, it minimized all the Cubase windows (project, MixConsole, Markers), but it did not minimize the one plug-in window that was open in my setup.
There is also another possibility in Windows 10, which is clicking in a slim area in the very right side of the Task Bar (see screenshot):
Note, though, that this minimizes all running applications, not just Cubase – it does get the plug-in window in my case. However, when you click again in that area to restore the screen, if you are running applications other than Cubase (e.g. I had Outlook and Edge and File Explorer running, with Outlook maximized on my left monitor and Edge maximized on the right), some of the other applications may be covering up Cubase, so it may take a few clicks to get Cubase back to the fore (for some reason, a click in the Cubase group on my task bar, then a click of the Cubase project window from there, does not work the first time, so I have to do it a second time – this has been a longstanding thing with Cubase, not unique to C13).
It appears the program group functionality should also be there in Windows 11, but I don’t have that to try. The notes I found say, " If you hover over the icon of one of the apps in the group, you’ll see both the app itself and the app group pop-up. You can then right click on the app group, and there’s the option to minimize/restore the group." It doesn’t look like Windows 12 has the same right corner of the Task Bar functionality, though.