First, I have to CLOSE (get rid of) all EXISTING windows explorer windows. So absolutely NO explorer windows running at all.
Once every single explorer window is removed (closed) - ie. no windows explorer windows in the background at all, I then start up an explorer window (fresh one). It is only then - a "gpupdate /force" will consistently bring the explorer window to the foreground.
Excellent work everybody. You have nailed it.
The procedure of closing all existing windows explorer windows was conveyed by Diplocaulus already.
If not already added, then I will just add that the multiple explorer pop-up situation can be reproduced using the same method. The only extra thing to do is to close all windows explorer windows to start with. Then open one explorer window to start with. Then right-click on any existing directory in that explorer window, and choose 'open in new window'. Do that a few times to get multiple different explorer windows open. And then go into the command window and do the 'gpupdate /force' thing. All of those background explorer windows will pop to the foreground.
FWIW (almost nothing if MSFT isn't even reading these posts), I tried this specific method and am unable to make multiple "File Explorer" windows pop-over with these instructions. Only the first window instance steals foreground/focus during "gpupdate /force."
Thank you