manjaro-chroot will not work for a system based on btrfs.
Depending on what you are trying to recover - most of it can be done without chrooting into the mountpoint.
pacman has some useful arguments which can be used to target the system behind the mountpoint.
Any configuration you may want to modify can be modified without chroot.
I requires some extra disicpline - but it can be done - I often forget to prefix with /mnt when I want edit edit e.g. mkinitcpio.conf - resulting in editing the rescue iso’s file system instead.
I clearly remember a very lengthy thread not so long ago where my memory was but to extreme test.
→ Totally broken system after December 2025 Stable Update
If you know which package(s) may be incomplete, then with the root mounted correct (btrfs or ext4)
Switch to root on the rescue system - assuming it is a Manjaro ISO.
Then ensure the database files are up-to-data on the ISO
pacman -Syy
The next command will use the mountpoint as system root and all actions will be inside the mountpoint
pacman -Syu --sysroot /mnt
To properly execute mkinitcpio and grub configuration update you need a working chroot
manjaro-chroot /mnt
mkinticpio -P
update-grub