The OP and most comments here are about an already-open File Explorer window coming from the background to the foreground. But in my case, I don't even use File Explorer (I have Directory Opus Pro) - at random, something (Windows?) will actually launch File Explorer. Is that the same bug or something different? It seems to do it in spurts - one day it will do it several times, and then not do it at all for days or even weeks. No, I'm not hitting any hotkeys - when it happened just now, I was watching a YouTube video in Firefox and not even touching the computer.
I am not aware of File Explorer being opened as part of this issue. Our issue is specifically an existing File Explorer window (or windows) being granted unwanted focus.
The issues might still be related - perhaps Directory Opus Pro uses File Explorer under the hood - but given you're not using File Explorer and your symptoms are different, you would be best to report your issue separately. Possibly to GPSoftware, too.