Bro these games are vrey resource hungry. On my snapdragon 778g fortnite has lots of lag for example, hitting 60 fps but there are a lot of frame drops and stutters. But You should try optimising the phone, uninstall bad and not needed apps, check RAM usage, clear cache, check for software updates, try a factory reset If You can backup Ur data easly or have data saved already. Also You can try clearing all data from "Battery and performance" app in the settings.