Can't boot into Windows after running EOS

(Dual-boot with Windows 11, separate ESPs)
I seem to be having the opposite problem of this thread: Cannot boot into EOS normally, can only boot after booting into Windows. Whenever I run one of my EOS instances and select Windows 11 Home after rebooting, the system can’t find the ESP. If I boot into Windows from the BIOS menu, the subsequent boots of Windows via GRUB work just fine.

Here is my current /etc/grub.d/40_custom (just the Windows 11 entry):

exec tail -n +3 $0
# This file provides an easy way to add custom menu entries.  Simply type the
# menu entries you want to add after this comment.  Be careful not to change
# the 'exec tail' line above.

menuentry '' {

# Microsoft Windows installations
menuentry 'Windows 11 Home' --class windows {
        search --fs-uuid --no-floppy --set=root 3040-4A9F
        chainloader (${root})/EFI/Microsoft/Boot/bootmgfw.efi

menuentry '' {

I recently updated my BIOS, so I’m wondering if I missed a setting somewhere. Since I can successfully mount my Windows partitions in EOS, Fastboot is not the issue.

This happens sometimes when updating the bios. Have you checked the boot order in the bios.

You wouldn’t want to run the os-prober and add the Windows Boot manager to grub.cfg instead?

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did you make sure that secure boot was disabled after the update?

@ricklinux - boot order is the same: EOS, then Windows
@pebcak - the 40_custom file I made adds the Windows boot entry just fine, no need for os-prober
@thefrog - Secure Boot has always been enabled

Just to reiterate: this only happens once, the first boot to Windows after running any of the (3) EOS installations. It’s like my BIOS needs to get slapped to remember where it is.

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I still think as @pebcak pointed out if you boot into EOS and then use os-prober and then run the grub update command might fix this.

Edit: Instead of using the custom grub entry!

Can you please explain how? If this was happening all the time, I’d tend to agree with you. But the entry works every time except for the first one, and that’s only after running EOS.

I believe this is a BIOS issue, not a GRUB/Secure Boot one.

I can’t explain it but i think it’s worth a try.

The UUID of Windows ESP may have changed. You can check them e.g. with command

lsblk -fm

Thanks for that. It was one of the first things I checked.