If I google for 'grub chainloading osx on apfs' the second hit is related to a broken os-prober and seemingly efi is involved. However, it's about another issue, at least hfs+ is used.
For a bootloader related request - especially since OSX is involved - consider to join https://lists.ubuntu.com/mailman/listinfo/ubuntu-users . On Ubuntu users there might be some OSX users subscribed who don't join the Lubuntu mailing list. -- Lubuntu-users mailing list Lubuntu-users@lists.ubuntu.com Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/lubuntu-users
