Since I've upgraded from PS 2017 to version 20.0.4, I'm seeing a grey 1 pixel line in the Thumbnail preview in the Layers panel - no matter which color theme and which thumbnail size I use. Is this supposed to indicate something?
My guess is that it's the same reason why an icon of hidden layers looks like on Windows this when zoomed in
And like this on Mac
And in CS6 the arrows of groups on Windows looked like it's a bit chipped:
Grid in newest Photoshops looks like this when zoomed it:
— to make perfectionists and people with OCD go crazy.