Each distro creates its own directory under /boot/efi/EFI, so I have /boot/efi/EFI/fedora,
/boot/efi/EFI/manjaro. /boot/efi/EFI/ubuntu.
And in each distro's directory, there's a set of the distro's own grub files,
including grub.cfg, that will bring up a normal grub menu let me boot any of my
installations. Selecting an individual distro's /boot/efi/EFI has to be done in the
boot setup screen or the 'System setup' entry in Fedora's grub menu