FIX THIS PROBLEM ALREADY, MICROSOFT
It's not just File Explorer doing it. I've noticed that Outlook has also started to randomly pop into the foreground just like File Explorer is.
I also tried the suggestion of disabling gpupdate from running at continuous intervals in the registry, but File Explorer still pops into the foreground anyway.
This is a completely unacceptable bug, and I'm long-past tired of typing and randomly opening programs or deleting files (or emails now) because a background window I was not interacting with suddenly steals focus, and now this problem is affecting Outlook windows, and I suspect there are other programs as well.
FIX THIS PROBLEM ALREADY, MICROSOFT