If commands suggested in post #3 are not working for you, download this script
https://gitlab.manjaro.org/packages/core/grub/-/raw/master/install-grub
script is still work-in-progress from Manjaro team but is working for my BIOS/MBR system
Install-grub: a new way to keep your EFI/MBR in-sync with grub package
OP has already tried install to MBR as shown in original screesnshot
The main problem for BIOS system users is confusing information from Manjaro Wiki
and misleading information from users that do not have accurate recall of how BIOS systems work