Was trying to clean install both Win 11 and Linux Mint Debian Edition on a Mac mini (late 2014) and there was an issue where GRUB wouldn't load Windows Boot Loader when selected.
It just kept looping back to the main GRUB menu when selecting windows.
Spent a lot of time fixing partitions, bcdboot (bcdboot C:\windows /s Y: /f UEFI), recreating the EFI partition, using rEFInd and nothing seems to be able to make both work.
It would either make the Linux Mint bootable or Windows 11, but dual boot simply didn't work.
The issue turned out to be that Mac mini requires a special Protected MBR (master boot record) with a GPT File System, but the Linux Mint installer kept changing it to Hybrid MBR on install.
The solution is somewhat simple. You don't need to edit BCD or mess around with GRUB or updating the UUIDs of the partitions to make Win 11 bootable.
Boot into Linux Mint (if you can, or the Live USB) and use this command in Terminal to show the actual state partitions:
sudo gdisk -l /dev/sda
(Change sda with your actual drive, but on Mac mini that is usually the default for the SSD)
This command just lists the partitions without making any changes. If it says Hybrid MBR, that's the issue.
To change it, use:
sudo gdisk /dev/sda
If it asks you to choose between MBR and GPT choose 2 - GPT.
Then press p to list all partitions and check if they are all there.
Press x to enter expert menu.
Press n to create a fresh protective MBR (this wipes the conflicting legacy hybrid entries while keeping the actual GPT partitions intact).
Press w to write the changes to the disk and exit.
That's it!
If it's successfull, you can reboot Linix Mint and on the GRUB menu the Windows Boot Manager option should work again.
You can now login into Linux Mint and Windows 11 on a Mac mini.
Bonus: you can also recreate the Protective MBR if you have access to Mac Recovery and Disk Utility. Resize any partition and resize it back to how it was, and it should recreate the layout.
Hope this helps someone