I'm working on an ASUS computer for a deceased colleague's widow. He had Fedora 28 on a HDD. I installed Debian 12 on an NVME drive. She also wanted Windoze 11 so I installed it on another NVME drive.
The boot mode was set to "legacy" but the Windoze installer DVD wouldn't even boot until it was changed to "UEFI" and then the Debian DVD wouldn't boot in UEFI so I changed the boot mode to UEFI/Legacy. The Windoze drive has a FAT32 EFI partition. update-grub doesn't see the Windoze install. I manually added menuitems in /etc/grub.d/40_custom using the partition's UUID (search --fs-uuid) and the partition's label (search --fs-label). None of them work. During boot, grub says the boot file doesn't exist, but when I boot Debian and look in the Windoze EFI partition, it's there. The Fedora and Debian installs are non-EFI, so there's no EFI grub. I tried to add the Debian partition to the Windoze boot manager using bcdedit and easyBCD but neither one could see it. If I want to have dual boot, instead of telling the BIOS which partition to boot, must I essentially start over with the Debian install i EFI mode (if I can find an installer DVD that will boot EFI)? I don't want to muck with the Fedora install. If I get a Debian EFI install done, will its grub-update be able to see the Fedora installation?
