This may actually be making the issue worse, not helping. Before you make any headway with sorting out this issue, you’ll have to undo the Grub Customizer installation.
Grub Customizer adds a file that is meant to help you remove it (it is kind of difficult to remove manually):
/etc/grub.d/backup/RESTORE_INSTRUCTIONS
I have seen it mentioned that certain permissions need to be adjusted prior to removing Grub Customizer with this method: dual boot - How to restore original grub config after uninstalling Grub Customizer in Ubuntu 22.04? - Ask Ubuntu
Another way would be to just toss the whole /etc/grub.d directory and start fresh.
Firstly, remove Grub Customizer if you haven’t already.
sudo pacman -Rns grub-customizer
Move the entire /etc/grub.d directory to backup.
sudo mv /etc/grub.d /etc/grub.d.bak
Reinstall the Grub package, to restore the needed files that have been moved to backup.
sudo pacman -S grub
Regenerate the Grub configuration file.
sudo update-grub
If you run into any errors during any of those steps, stop and address them before proceeding–otherwise you may be unable to boot, and you will need to repair your system from the live environment.
When you are ready, reboot to test that all is well. Then go ahead and delete the old directory that was moved to backup.
sudo rm -rf /etc/grub.d.bak
Check for lingering files is on the EFI partition. Removing a distro by overwriting the partition it is installed on leaves behind the directory Grub installed at /boot/efi/EFI.
sudo ls -l /boot/efi/EFI
Grub will find any grubx64.efi files in these directories and add them to your boot menu, even if the installation itself is long gone (Grub has no way of knowing). If you see any abandoned installations in this directory, go ahead and delete them. Afterward, regenerate the Grub configuration file again.
Check for old boot variables that can be deleted.
efibootmgr
This will show the boot variables currently on your system. Identify the ones no longer needed and delete them.
sudo efibootmgr -b # -B
Substitute “#” in the command above for the boot variable you wish to delete. If you have multiple boot variables for Garuda and you aren’t sure which one you are supposed to keep, you can delete them all and then re-run the Grub installation routine.
sudo grub-install
Then regenerate the configuration file again.
sudo update-grub