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;
https://en.wikipedia.org/wiki/EFI_system_partition#Overview
tl;dr: don't mess with it.
Welcome to the community for Windows 11, Microsoft's latest computer operating system.
Rules:
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;
https://en.wikipedia.org/wiki/EFI_system_partition#Overview
tl;dr: don't mess with it.
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.
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.
Fix Fortnite, NOT your partitions.