When changing a folder, the button's highlight changes its size. Please see the video.
Is it bug or feature?
Only when Preferences / Toolbars / Options / Move top-row toolbars into the window title bar is on, correct?
No:
It bugs in every mode.
Video capturing software (Microsoft Xbox Game Bar?) just crops-out the window title bar...
I was initially able to reproduce this with the top-toolbar option on, but not with it off.
Today I can't reproduce the problem at all, even on the machine I saw the issue with before.
Is it still happening for you?
(FWIW, I did notice some strange graphical problems recently which went away after updating my NVidia driver. I suspect there was a bad driver version either from NVidia or pushed through Windows update which had some bugs in it. But I don't know if that would also be related to this.)
Yes, it still happens. And I never use top-toolbar enabled yet.
My video card is integrated Intel UHD Graphics 620. I had no any video issues yet before. Video-driver is up to date by Windows.
Can I give you additional info if it would help?
Does it only happen when the window isn't wide enough to show all the toolbars? I think that may be a factor, but not 100% sure yet.
I don't think so. See the video. As you can see all the toolbars are fully expanded by width (but all of them are in one single row).
I noticed one more feature: if press LMB on different objects consistently (file - folder, folder - empty space, folder - file) button's highlight twitches twice, while if objects are the same (file - file, or folder - folder) it twitches ones.
BTW, the lister still has the window title bar:
Does it make a difference if the viewer pane is closed?
Nop...