If you have read the fine announcement before updating
You would have seen kernel 6.16 is non-existent anymore. In theory linux-meta had to solve this automatically for you… don’t know what happened (maybe you uninstalled it youself?).
Anyways…boot live usb, chroot manually for btrfs (there is a recent tutorial in the tutorial section)
https://forum.manjaro.org/t/root-tip-recovery-basic-manjaro-linux-rescue-and-recovery/
and install a kernel.
pacman -S linux618
And regenerate grub menu
update-grub
Which is the shortened alias from
grub-mkconfig -o /boot/grub/grub.cfg