On 16/02/2023 22:25, Joe wrote:
Stretch installed perfectly dual-boot with Win 10 on an EFI Acer netbook, but upgrading to Buster broke booting to grub. It actually broke EFI booting completely, but I've been able to restore booting at least to Windows. And yes, I've tried everything the Net can suggest.
UEFI implementation by particular vendor may be buggy. E.g. an old HP laptop may be booted up either when it is configured to load a specific .efi file or when directory structures on EFI internal hard drive partition follows layout designed for a removable storage. It ignores most of EFI variables, so e.g. it is better to remove fbx.efi fallback intended to fix boot order.
When you have learned such stuff, it is easy to fix boot. Unfortunately pieces of the puzzle was spread over multiple resources.
I am not surprised that installer was unable to apply proper workarounds on particular machine. I have heard that vendors may add code intended to ensure booting Windows, but other OSes may be out of luck using the same file layout.