When you format the FAT32 partition using Windows 10, or execute BOOTSECT.EXE /nt60 on the partition, it writes an NT6 bootsector to the partition which seeks & loads BOOTMGR.
When you format the FAT32 partition using DOS, or execute SYS.COM on the partition, that would write a DOS bootsector to the partition which seeks & loads IO.SYS.
When you SYSLINUX the target FAT32 partition using either Windows or Linux, that writes a Syslinux bootsector to the partition (also writes ldlinux.sys & ldlinux.c32 files) which seeks & loads ldlinux.sys (and ldlinux.c32). Which then searches for the syslinux folder and a syslinux.cfg file inside. Also ldlinux.c32 and any .C32 files in the syslinux folder need to be the same version that you SYSLINUX'ed the partition bootsector with.
With the full fileset of the live Linux distribution copied to the bootable Syslinux'ed FAT32 USB drive, change the name of the isolinux folder to syslinux and inside your new syslinux folder, change the name of isolinux.cfg to syslinux.cfg.
A good live distribution will then boot from a Syslinux'ed USB FAT32 partition using a syslinux folder, instead of from a DVD using an isolinux folder.
Comments
If you are feeling brave it can be done in Windows without any extra software...
1. Use DISKPART to wipe the USB storage, and create a new active partition as FAT32
2. Use Windows Explorer to open the ISO and copy all the files to the new blank USB Storage.
Works for most 'live' DVD/USB based distros supplied as ISOs, but not-so-much for .img files with multiple partitions (like Raspbian)
When you format the FAT32 partition using Windows 10, or execute BOOTSECT.EXE /nt60 on the partition, it writes an NT6 bootsector to the partition which seeks & loads BOOTMGR.
When you format the FAT32 partition using DOS, or execute SYS.COM on the partition, that would write a DOS bootsector to the partition which seeks & loads IO.SYS.
When you SYSLINUX the target FAT32 partition using either Windows or Linux, that writes a Syslinux bootsector to the partition (also writes ldlinux.sys & ldlinux.c32 files) which seeks & loads ldlinux.sys (and ldlinux.c32). Which then searches for the syslinux folder and a syslinux.cfg file inside. Also ldlinux.c32 and any .C32 files in the syslinux folder need to be the same version that you SYSLINUX'ed the partition bootsector with.
With the full fileset of the live Linux distribution copied to the bootable Syslinux'ed FAT32 USB drive, change the name of the isolinux folder to syslinux and inside your new syslinux folder, change the name of isolinux.cfg to syslinux.cfg.
A good live distribution will then boot from a Syslinux'ed USB FAT32 partition using a syslinux folder, instead of from a DVD using an isolinux folder.