Why does the game look better in borderless-window mode compared to fullscreen?

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

last edited by SirPenetrator

What is your res scale at?

@sirpenetrator could be that then right? I do not see any difference both are 1440p