Go to fortnite options and select directx 11 instead of 12 and apply , then it restart the game and doublecheck its off. If that dont help, verify fortnite files from the epic games launcher (google how).
Check also fixes from this video :
View: https://www.youtube.com/watch?v=n1zfVQo112E
First try the battleeye uninstall / install then easy anticheat repair / uninstall / install. If that wont work then update your graphics drivers.
If none of this help, try to lock your gpu to use GEN3 pcie instead of GEN4 or auto setting from BIOS, (google is your friend for this one, rememebr all the manufactors of motherboards have different kind of bios settings , you will find out how)