Keep this between 80% and 100% . Lowering it further can significantly boost FPS but will make the game look blurry.
Match this to your monitor's refresh rate (e.g., 144 FPS for a 144Hz monitor). Setting it to "Unlimited" can cause inconsistent performance and overheating. How To Fix FPS Drops & Lag in Fortnite Season 3...
Set View Distance to Medium (to see players) while keeping Shadows, Textures, and Effects on Low or Off . Keep this between 80% and 100%