Compatibility mode is a feature where Windows mimics an earlier version. Doing this can solve some issues with drivers that are incompatible with a newer version of Windows.
- Navigate to your Fortnite binaries directory (Default: C:\Program Files\Epic Games\Fortnite\FortniteGame\Binaries\Win64\)
- Locate FortniteClient-Win64-Shipping.exe.
- Right-click it, and then click Properties.
- Click Compatibility.
- Check the box next to Run this program in compatibility mode for.
- Make sure Windows 8 is selected.
- Check the box next to Disable fullscreen optimizations.
- Click Apply.
- Click OK.
- Relaunch Fortnite.
If this did not help solve the issue try the next step in our troubleshooting: How do I update my Microsoft .NET Framework to play Fortnite?