The EFI system partition is formatted with a file system whose specification is based on the FAT file system and maintained as part of the UEFI specification;
That is your boot partition. You can’t / wouldn’t want to change the filesystem of that partition. You could very easily cause your Windows OS to not load.
Why do you want to do that? That's your boot partition (the thing the motherboard looks at to determine where the rest of the OS is). Changing that format scheme could break your install.
The EFI system partition is formatted with a file system whose specification is based on the FAT file system and maintained as part of the UEFI specification
What's the exact error message you receive from fortnight? That's what you need to resolve, cause there's nothing wrong with what you've originally posted, but if you do find a way to do what you originally asked you WILL break your system.
The boot sequence looks for a FAT based partition to boot from. If you convert it to NTFS, then your system won't boot up. The fact that Fortnite won't install should tell you that you are doing something wrong with Fortnite. In fact, NO game should ever mess with your installation like that.