I've had the problem for about 3 weeks
I've tried everything: check, repair, and reinstall Fortnite
Delete and reinstall the Epic Games Launcher
Sign in with a different Epic account
Reinstall graphics driver
With other Epic Games games it works without problems, only Fortnite does not start
When I click on it, it says something about synchronizing the cloud, then it is running and then I click the start button again.
Have you signed in to your PC with OneDrive? Had the same problem and then we went again
No, with my Epic account
Generally log in to the PC with OneDrive, then everything started again for me
Unfortunately it still doesn't work