After a lot of digging, I figured it out! Since I didn’t have a ramdisk or kernel images in my /boot directory, update-grub generated a configuration that searched for a kernel on the NVME drive, which GRUB cannot see. So to get GRUB to boot the linux kernel right away, I had to manually set up the initial ramdisk environment using mkinitcpio:
# Enter chroot using live ISO
sudo mkdir -p /mnt/broken
sudo mount /dev/nvme0n1p1 /mnt/broken
sudo garuda-chroot /mnt/broken/@
# Mount the boot volume (the drive was at sda1 this time)
mount /dev/sda1 /boot
# Install kernel and generate .preset files in /etc/mkinitcpio.d
pacman -S linux-zen
ls /etc/mkinitcpio.d
linux-zen.preset
# Create initial ramdisk and check that the kernel and image files are in /boot
mkinitcpio -p linux-zen
ls /boot
grub initramfs-linux-zen.img memtest86+
initramfs-linux-zen-fallback.img intel-ucode.img vmlinuz-linux-zen
# Re-install and update GRUB
grub-install /dev/sda
update-grub
And finally, after exiting chroot and rebooting, I had a working system again! It seems the cause of this issue was that when updating my system, the .preset files in /etc/mkinitcpio.d didn’t get generated for some reason. So when the GRUB configuration was updated, I didn’t have an initial ramdisk environment, leaving me with an unbootable system.