Just stumbled upon this after converting a system from Legacy Boot to UEFI (boot into live, sort out partitions, remove grub-pc, install grub-efi, reboot, reconfigure bios).
After running `apt install grub-efi` and rebooting, although the former fails with the error mentioned above, debian correctly shows up in my boot menu and I can boot from it. This is the partition tree on my boot devices: nvme0n1 259:0 0 119.2G 0 disk ├─nvme0n1p1 259:2 0 512M 0 part │ └─md10 9:10 0 512M 0 raid1 /boot/efi ├─nvme0n1p2 259:3 0 512M 0 part │ └─md11 9:11 0 511M 0 raid1 /boot └─nvme0n1p3 259:4 0 118.2G 0 part └─md12 9:12 0 118.2G 0 raid1 └─nvme-root 253:0 0 25G 0 lvm / nvme1n1 259:1 0 119.2G 0 disk ├─nvme1n1p1 259:5 0 512M 0 part │ └─md10 9:10 0 512M 0 raid1 /boot/efi ├─nvme1n1p2 259:6 0 512M 0 part │ └─md11 9:11 0 511M 0 raid1 /boot └─nvme1n1p3 259:7 0 118.2G 0 part └─md12 9:12 0 118.2G 0 raid1 └─nvme-root 253:0 0 25G 0 lvm / I ended up cleaning UEFI's config up and adding the second drive to the boot sequence with: efibootmgr -c -d /dev/nvme0n1 -p 1 -L "Debian nvme0n1" -l \\EFI\\debian\\grubx64.efi efibootmgr -c -d /dev/nvme1n1 -p 1 -L "Debian nvme1n1" -l \\EFI\\debian\\grubx64.efi Although everything seems to be working as it should, it would be good if `grub2-install` could handle this to prevent unexpected errors/failures during installation, upgrades or even just minor updates. Firmware info requested above (although I'm fairly sure this is not firmware-specific): Vendor: American Megatrends Inc. Version: 1.3 Release Date: 11/25/2020 Address: 0xF0000 Runtime Size: 64 kB ROM Size: 32 MB [...] BIOS Revision: 5.14 -- Giorgio Bonfiglio www: grg.pw email: m...@grg.pw