How to Set Up a Backup GRUB for Manjaro if SSD Isn’t Detected?

You can back up the EFI partition on a different location if you'd like, but make sure you're booting the installer in UEFI mode instead of legacy mode—getting that wrong can mess with your installation! Ideally, each OS should have its own EFI partition on its drive. I recommend looking into how UEFI booting operates and how the EFI partition works. It might not be overly complex, but many people don’t realize how it all ties together.

Most Linux installers tend to use the existing EFI partition, which often ends up being the one on your Windows SSD. If the SSD fails or isn't connected, your Linux install won't boot since it can't find that EFI partition. A good workaround is to disconnect the Windows drive during the installation of Manjaro. If that's not feasible, you could try creating a new EFI partition on your hard drive while installing Manjaro to make it independent from the SSD. It's a little involved, but it will ultimately help ensure that the bootloader works when the SSD isn't available.

I see where you're coming from. The concern is having a bootloader that would be available if the SSD is disconnected. You might want to make sure to set up GRUB on your hard drive's EFI partition instead. This way, even if the SSD fails, Manjaro will still have its own bootloader intact. But keep in mind, you'll need to go through some steps to ensure that everything is configured properly.