Please start the Epic Games Launcher using Right Click “Run as Administrator”
The other known problem is lack of Virtual Memory
How to manually add a Virtual Memory 64GB Pagefile.sys
Some times creating a new account to see if that is the problem and “Run As Administrator” when starting Epic Games Launcher or change the short cut properties to
“Run As Administrator” and then launch Fortnite or UEFN
Verify your installation with
How do I verify game files in the Epic Games Launcher? - Epic Games Store Support