Grub menu not showing up on boot after firmware update

Solution 1:

There can be a very simple fix (see the source), but in a nutshell, from a Windows Terminal with admin rights, run the command:

bcdedit /set {bootmgr} path \EFI\ubuntu\grubx64.efi

Warning: this is of course specific to Ubuntu. Other distros will have different paths.

If the command succeeds, you can reboot and grub should appear. Otherwise, if the command fails, run either:

# cancel the previous command:
bcdedit /deletevalue {bootmgr} path \EFI\ubuntu\grubx64.efi

# or, to explicitly revert to Windows boot manager:
bcdedit /set {bootmgr} path \EFI\Microsoft\Boot\bootmgfw.efi

Note: Secure boot must be deactivated.

Solution 2:

According to comments above, it seems that several ways can be used to solve the issue.

In case the EFI System Partition - ESP has been marked as hidden, this flag has to be removed in order to run boot-repair.

You may also have to unlock secure boot in BIOS in order to run boot-repair.

Bottom line, boot-repair is the a solution, but running it may require some preliminary actions.