Getting a bootable win10 usb is a very touchy exercise.
See the topic
My response 58/64 has the method that works. I can recall it took me ages to arrive at that recipe.
The FOSS article needs revamping.
You have correctly worked out that the win10 file is too big for a fat filesystem
You have to use ntfs on the usb drive, and you have to add a bootloader, because the win10 iso file is not a hybrid iso file, ie it will boot if copied to a dvd, but will not boot if copied to a usb drive.
It is nothing short of an absolute mess
Man dumping a Linux ISO on a thumb stick is a no brainer!
Because Linux iso’s are mostly hybrid iso’s… they contain a bootloader… and because they use ext filesystem