Try chroot from garuda-welcome or How to chroot Garuda Linux
and not forget
update-grub
After reboot you must maybe change the /etc/default/grub file.
# Probing for other operating systems is disabled for security reasons. Read
# documentation on GRUB_DISABLE_OS_PROBER, if still want to enable this
# functionality install os-prober and uncomment to detect and include other
# operating systems.
GRUB_DISABLE_OS_PROBER=false