I did come up with one observation. With only ONE explorer window open, my system went for over 30 hours without stealing focus. As soon as I foolishly allowed TWO explorer windows to be open, whamo, the problem reappeared.
Glad that's working for you. In my case, the problem persists whether it's just one open File Explorer window or several.
Side note, if I have several open File Explorers and I'm editing file names in one, it's not unusual for another File Explorer to suddenly take it's place.