System file /boot/grub/grub.cfg has this comment:
#
# DO NOT EDIT THIS FILE
#
# It is automatically generated by grub-mkconfig using templates
# from /etc/grub.d and settings from /etc/default/grub
#
So changes to this file would be overwritten whenever GRUB is updated
But if GRUB configuration changes are made in file /etc/default/grub changes are not implemented until GRUB is updated
Users coming from other distributions may not realise that Manjaro GRUB does not force the first menuentry in GRUB as the default option
Manjaro uses 2 options in /etc/default/grub
GRUB_DEFAULT=saved
GRUB_SAVED_DEFAULT=saved
If a user chooses to boot from something other than the first menuentry, GRUB will continue to boot the user selected menuentry
But /etc/default/grub can also be reconfigured to boot a specific named menuentry
Latest update messed up my GRUB Menu
The option GRUB_DEFAULT
can be edited to use a specific number or name from the menuentry list on GRUB
Using the menuentry number is not good for the Windows boot option because the number will change if Manjaro kernels are added or removed from the list in GRUB
If OP wanted grub to boot Windows, option would be something like
GRUB_DEFAULT="Windows Boot Manager (on /dev/sda2/)"
I would not recommend editing anything in /etc/grub.d/ to change order of menuentry items in GRUB because I experienced problems with updates following changes to /etc/grub.d/
( grub-customizer
)
I had this problem over 4 years ago but I still recall the hassles of repairing GRUB
But since I have only changed GRUB configuration in /boot/grub/grub.cfg
I have had no problems with GRUB updating
(except for getting an occasional /boot/grub/grub.cfg.pacnew
to check and merge new settings)
If you still intend to modify GRUB configuration to change the order of menuentry items I recommend you make backup copies of any files before implementing changes