By default, Grub will be installed with the bootloader ID “Garuda”, which will add the bootloader files to /boot/efi/EFI/Garuda. If your two installations are sharing an EFI partition, the second installation will have overwritten this directory from the first one.
To set them up with separate bootloader files, boot to whichever one is still working (Hyprland I guess), and rename this directory to something else, for example “garuda_hyprland”:
sudo mv /boot/efi/EFI/Garuda /boot/efi/EFI/garuda_hyprland
Next, change the GRUB_DISTRIBUTOR= line in /etc/default/grub to match whatever you just named the boot directory in /boot/efi/EFI/.
sudo micro /etc/default/grub
GRUB_DISTRIBUTOR="garuda_hyprland"
Run the Grub installation script. Probably grub-install or grub-install --no-nvram (to not add another NVRAM entry) will be enough. If you are not sure, or want to learn more about the options, refer to the document here: GRUB - ArchWiki
sudo grub-install --no-nvram
Regenerate the Grub configuration file.
sudo update-grub
Next, you will have to reinstall Grub on the first installation from a chroot as described here: How to chroot Garuda Linux
After you get Grub reinstalled on the first installation, you should be able to boot to either one because they will have separate bootloader files.