Your Manjaro is installed on a BTRFS filesystem.
You would need a patched os-prober to detect the systems installed on BTRFS.
Something like the following package from AUR:
Or build Manjaro’s own and install it on EnOS:
Please note that if you choose the second option, you would need to keep track of the updates yourself.
Another option would be to let Manjaro be in charge of the booting process.