> Windows installer images have some files too large … I believe the USB stick needs to be exFAT formatted
That’s true. I forgot!
While it’s not part of the UEFI spec many (most?) consumer BIOSes will be able to UEFI boot from NTFS as well, so formatting as that might also be an option.
Both that and exfat should be easy to do on Linux. No idea about MacOS.
Which brings me to
> too large for most tools to understand
This I don’t understand. What tools? What tools do you need beside “cp”?
I don’t know if you can just copy the files over. It seems you also need to make the USB stick bootable?
There’s dozens of guides on doing this on a Mac, they all seem outdated. I found a tool called WinDiskWriter on GitHub and it was the only GUI tool that worked.
Suspect there’s more to it than just cp. There’s wimlib too for handling the larger files on the install ISO.
TLDR: UEFI just checks in NVRAM for pre-existing boot-configs (stored paths to EFI-executables for installed operating systems) and if doing "dynamic" booting from some random media, it checks if the the volume has a EFI-executable for the given architecture (for instance in \BOOT\bootx64.efi for Intel x64), and if it does, it loads that file.
UEFI usually boots straight into native long mode without any weird 8086 compatibility modes being employed (which the OS then has to unroll), so for the OS its simpler to deal with.
It can also serve as a multi-boot menu on machines which has several OSes installed.
It often comes with a MS-DOS like "UEFI Shell" you can boot into... To manage UEFI itself. So if something doesn't boot, you can just boot into the shell instead and try to fix things from there.
It may sound complex, but once you get into it, its really much easier to work with that legacy MBR boot, and all the "magic" things you have to do their to get things booting.
That’s true. I forgot!
While it’s not part of the UEFI spec many (most?) consumer BIOSes will be able to UEFI boot from NTFS as well, so formatting as that might also be an option.
Both that and exfat should be easy to do on Linux. No idea about MacOS.
Which brings me to
> too large for most tools to understand
This I don’t understand. What tools? What tools do you need beside “cp”?