with btrfs , yo ucant use command manjro-chroot
you have to use this one
you can use manjaro-chroot this way
( recheck disks partitions before )
sudo mount -o subvol=@ /dev/sdaX /mnt
manjaro-chroot /mnt
done
or
sudo mount /dev/sdaX /mnt
manjaro-chroot /mnt/@
if you want to install grub
for uefi
you can
mount efi partition before hand
consider
/dev/sdaX is root partition
/dev/sdaY is efi partition
sudo mount /dev/sdaX /mnt
sudo mount /dev/sdaY /mnt/@/boot/efi
manjaro-chroot /mnt/@