FAT32, exFAT and NTFS compared
These are three file systems you meet on USB drives. FAT32 works almost everywhere but cannot store a single file larger than 4 GB. exFAT removes that limit. NTFS is the main Windows file system.
Why it matters when you use a bootable USB drive
A UEFI boot drive normally uses FAT32. A large ISO may not fit on it, which is why many tools split files or use a different layout.