Ubuntu, and I presume other debian-derived distros, supports
--no-nvram, but it's not
enough. There's a debconf config:
grub2/update_nvram: false
but when APT gets a new version of grub, and the post install script
runs, grub-install
doesn't get the memo and still overwrites grubx64.efi in the EFI
partition, pointing
the boot directory back to where it thinks it should go.
My solution for this is make a copy of ubuntu/grubx64.efi when it has the boot
directory I want (usually to a dedicated, independent of any distro,
grub partition or
subvolume) and set an EFI boot entry that uses my copy. Now any Ubuntu distro's
grub-install won't interfere.