When I switch between "borderless-window" mode and "fullscreen" I notice that the game looks very blurry/washed out in "fullscreen" but when switching to "borderless-window" everything seems to be smoothened out with nice edges etc.
I guess it's a bug?
Could this be the possible explanation:
When in Fullscreen the game uses my settings with Res @1080p
When using borderless-window the game uses my settings from the Desktop @2560x1440p