I am getting the same issue. It is not when a video is playing. I can be sitting here working on a Word document and suddenly the File Explorer window pops to the front, with the cursor blinking in the search box.
It happens at extremely irregular times, as the first person said, it could be four minutes before it happens again, or four days. It just happened to me half an hour ago while I was sitting here talking to a colleague - I didn't have my hands on the keys or the mouse, I have a wired mouse and keyboard because those battery ones are terrible, and darned if the File window didn't pop from being minimized to the front of the screen with the cursor blinking in the search box again.
Have you ever had that thing where your trackpad is on even though you're using the mouse, and if you bump it, the selected window changes? It's a lot like that, except we don't have trackpads here at the office. And it happens when you aren't even touching the computer in any way. So it isn't a trackpad error and it isn't that I bumped the mouse accidentally.
Yea, I don't think it's specific to watching a video in my case either, it's just that I usually have file explorer open after selecting a video file.
I never noticed the cursor flashing in the search box but I'll watch out for it the next time.
I'm on AMD, 5800X and an RTX 3080, just wondering if your specs are similar?
But yes, it seems totally and absolutely random, and I'm pretty sure that it carried over from my last fresh install as well which probably rules out a Windows OS issue.
I also have Power Toys installed, several photo editing tools (photoshop, etc), and some ASUS and LG driver software, Argus monitor, and I think Hyper-V is running in the background too, if any of those ring a bell with you?