Why does Stretched Resolution not work in Fortnite?

I just wanted to test how to stretched in Fortnite spiel.ich I have the setting everything is done correctly -have set all the values to 1440 (that's the one I want to play) have changed in the settings (NVIDIA) everything correctly and the screen was also gestreched.Wenn I start Fortniten the screen is synonymous gestreched, but as soon as I'm really in the game (ie in the lobby) everything is back to normal and the desktop resolution is back to normal 1090 × 1080th What do you do Am I wrong? I also know that it works because I've tried it about half a year ago.

You have to turn off in the settings full screen, then it works (was with me like that)

Turn off? In the tutorials everybody says that it has to be on

It must be from full frame to full screen in the window.