Halo and when I'm in fortnite and click on the minimize button the game stops.
What could be the reason
This is because you may have a bad laptop / PC / console.
I'm not familiar with Fortnite, but with other games it helps with the graphics settings on borderless windows instead of full screen
Yep, perfect answer imho.
Or. Minimize button? What is that?
It wasn't because of the pc but because of the settings. I thought I have an nvidia 2070 super graphics card