Always cleanest to have 2 disks:
- disk 1: Pure Windows installation without GRUB (as if Linux never installed)
- disk 2: Any other Linux partitions, along with GRUB and GRUB menu
Physically disconnect disk 1 while building disk2 and installing the other OS images, then, when satisfied,
- reconnect disk 1
- [IMPORTANT] set disk 2 as first choice in boot priority for BIOS/UEFI
- boot system
- open session on Linux of choice
- run update-grub
- reboot
- GRUB menu should now offer Windows as the last choice among boot options
- choose whichever OS to load up
That way, GRUB doesn’t “mess up” Windows disk and Windows doesn’t tamper with GRUB setup (physically on disk 2)
