Fortnite full screen mode not working?

I have a problem with Fortnite. When I switch to full screen I can't click anything for about 7 seconds or only press if I keep pressing the Windows key. The resolution is there (option). After these 7 seconds, the game automatically changes to full screen in the window. I've only played full screen so far and everything worked. I would actually play it full screen in the window but in this mode my fps don't get higher than 60 even though I set it to 144 fps. (I have a good PC and before that I could always play at 160 fps…) I would be happy to get an answer.

I would uninstall Fortnite and leave it that way and do something clever.