This question - Is it possible to turn visible the invisible window's borders of Windows 10? - does not appear to address the same issue. Things appear to have got (even) worse.
I just underwent a dreaded update.
I now notice that the ghastly aesthetics now apparently mean that some applications (e.g. Windows Explorer) now have no frame whatsoever, not even a 1-pixel border, when they have focus.
This (surprise!) frequently makes it difficult to know where the window in question ends and another begins.
Is there anything at all that can be done about this? I have searched quite a bit. I found that you can set the border colour (1-pixel border) to a custom colour supposedly. So I did that. But it only applies to the frame of Windows Explorer when it does not have focus (and when it is stationary).
later