It has been for a while that my desktop PC was not showing the GRUB2 menu.
Besides, I noticed that there was a warning message during the execution of
Warning: Setting GRUB_TIMEOUT to a non-zero value when GRUB_HIDDEN_TIMEOUT is set is no longer supported.
After checking the manual, I learned that we can fix the problem by removing
following line from
And update the GRUB with:
$ sudo update-grub
After rebooting, GRUB should work now.