Just edited etc/default/grub and added loglevel=3 to the end of the `` line and executed sudo update-grub. Rebooted. And now the message is gone on both shutdown and reboot’s much faster. All while startup seems unaffected. And I did it again, to make sure it wasn’t a fluke, and it stuck!
Nice but apparently it would hide some messages then (see the log level link in my post). I still didn’t have a chance to try on the friend laptop yet but I’ll apply it then next time I will have a chance.
//EDIT: I think log level by default in Manjaro is 4 for info
Which line? the GRUB_CMDLINE_LINUX="" line or a new empty line?
# If you want to enable the save default function, uncomment the following
# line, and set GRUB_DEFAULT to saved.
# Preload both GPT and MBR modules so that they are not missed
# Uncomment to enable booting from LUKS encrypted devices
# Uncomment to use basic console
# Uncomment to disable graphical terminal
# The resolution used on graphical terminal
# note that you can use only modes which your graphic card supports via VBE
# you can see them in real GRUB with the command 'videoinfo'
# Uncomment to allow the kernel use the same resolution used by grub
# Uncomment if you want GRUB to pass to the Linux kernel the old parameter
# format "root=/dev/xxx" instead of "root=/dev/disk/by-uuid/xxx"
# Uncomment to disable generation of recovery mode menu entries
# Uncomment this option to enable os-prober execution in the grub-mkconfig command
# Uncomment and set to the desired menu colors. Used by normal and wallpaper
# modes only. Entries specified as foreground/background.
# Uncomment one of them for the gfx desired, a image background or a gfxtheme
# Uncomment to get a beep at GRUB start
#GRUB_INIT_TUNE="480 440 1"
# Uncomment to ensure that the root filesystem is mounted read-only so that
# systemd-fsck can run the check automatically. We use 'fsck' by default, which
# needs 'rw' as boot parameter, to avoid delay in boot-time. 'fsck' needs to be
# removed from 'mkinitcpio.conf' to make 'systemd-fsck' work.
# See also Arch-Wiki: https://wiki.archlinux.org/index.php/Fsck#Boot_time_checking