I'm currently working on a tripple-boot system with Ubuntu 18.04, macOS and Windows. The standard bootloader that the firmware (ASUS Impact VII, APTIO-based EFI) is supposed to launch is Clover. Clover then runs GRUB 2, Apple's EFI bootloader or the Windows bootloader.
The problem is that when I update the standard grub-efi packages on my Ubuntu 18.04 system via apt/dpkg, the EFI firmware will proceed to boot GRUB instead of Clover on the next reboot.
I understand that this happens because the GRUB setup changes the EFI variables to make itself the default bootloader. More specifically it does not pass
--no-nvram to grub-install.
How can I make the GRUB EFI packages not modify the EFI boot variables via grub-install, so that Clover remains the default bootloader?