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How do I get Grub to boot on Windows?
That should be the bare-bones UEFI chainloader entry for Windows. Just replace xxxx-xxxx with the actual Windows ESP filesystem UUID. After editing the file, run update-grub as root. Then set the default boot option to debian and you should have your boot menu.
By default, GRUB will show the menu if there is a second operating system installed. If only Ubuntu is installed, then GRUB will generally load Ubuntu without showing the menu. To reconfigure GRUB to always show a menu:
How long does it take to change boot order in Grub?
This will edit the Grub menu and you can see the changed boot order at the next restart. If you do not interact with the grub menu at the boot time, it takes 10 seconds to boot into the default operating system.
How to configure GRUB menu entry for Windows?
Once you know the UUID, you can configure a custom GRUB menu entry for Windows, by adding these lines to the end of /etc/grub.d/40_custom: That should be the bare-bones UEFI chainloader entry for Windows. Just replace xxxx-xxxx with the actual Windows ESP filesystem UUID. After editing the file, run update-grub as root.
What to do if Grub does not show on Windows 10?
Make sure Linux sees your SSD, then run update-grub as root. If it doesn’t say it detected Windows, run blkid as root: it should report the UUIDs of all your filesystems and partitions. Find the filesystem UUID of the Windows ESP on the SSD.
Why does my computer not boot with Debian?
As the Debian Wiki says: Many UEFI firmware implementations are unfortunately buggy, as mentioned earlier. Despite the specification for boot entries and boot order being quite clear about how things should work, there are lots of systems in the wild which get it wrong. Some systems simply ignore valid requests to add new boot entries.