Instead of creating a new thread, I decided to continue this one.

The computer does not show a BIOS entry for the disk anymore. The output of efibootmgr now is
and I do not see anywhere a 003D or 2003 entry (non under /sys/firmware/efi/efivars).
Edit. And I cannot remove those two entries
/Edit

I believe here there should have been two directories, the one listed below and a "BOOT" directory. Am I wrong?
And no, I did not delete anything. Edit2. Since yesterday. /Edit2.

The only thing that was done to the computer since the last known good boot (yesterday) was a grub-- package upgrade
Finally, thanks to a link provided in another thread here, is this what I should do?
with /dev/sda1 being my EFI partition (/boot/efi mount point).


Right now I can boot manually from BIOS through a sequence of "Boot from EFI file" > "EFI-some-string" > EFI > debian > grubx64.efi, which loads the grub menu.

With some more reading I ended up with this line
And i guess "-p 1" is not needed in this case.

Mine are all debian10, debian11 or debian12. A BOOT is there as a fallback, so if it's missing, it doesn't matter if there's another that produces the desired results.

Was it a full-upgrade that appeared to fully complete?

With a possible exception of -L, all good. If /etc/default/grub's GRUB_DISTRIBUTOR= contains `lsb_release -i -s 2> /dev/null || echo Debian` and lsb_release -i -s 2> /dev/null || echo Debian produces "Debian", then yes. If it produces "debian", then no, IIUC. The ESP is not a case sensitive filesystem, but because of the presence of GRUB, and the fact that all other directories in /boot/efi/EFI/ on mine are lower case only, I'm not sure for this purpose whether or not Grub is sufficiently sophisticated in this area to not care about the case of the directory name that contains grubx64.efi.

None of my GRUB_DISTRIBUTOR=s contain `lsb_release -i -s 2> /dev/null || echo Debian`. Because I multiboot, I change every one to the form above, e.g. ="debian11". This keeps each installation's /boot/efi/EFI/ directory unique, which prevents overwrites resulting from upgrades.

I believe so.

I've never tried not quoting what follows -L.

Just fixed it.

The BOOT directory is missing, and there is none at my stable computer as well.

This system has all possible Debian sources in, including unstable and experimental; you might call it a rolling Debian release.
I had another package that came in before the fix and did not fix it either. It was "grub-efi-amd64-signed".

From the link in another thread (which I think it was provided by you): boot manager display label (defaults to "Linux") ; { and this should be the same as stored in (grep GRUB_DISTRIBUTOR /etc/default/grub) }
Which in my case it is Debian with a capital.
I have read some ten threads with examples, some have quotes and some not. If there are no spaces then I think that quotes are not necessary.

Anyway, the line was correct, it was installing an entry
Boot0000* Debian HD(1,GPT,a13692c0-aa2c-4bec-8669-a98f290251d6,0x800,0x200000)/File(EFIdebiangrubx64.efi)
which was probably removed at shutdown. On reboot the entry was missing.

Then I went in the BIOS. Disabled the "Internal Network Adapter Boot", which I do not use anyway, and enabled "Legacy Support".
Edit. At his point I let it boot and ended in a blank page with "GRUB" on the top left. No input no cursor. Rebooted, went to BIOS boot options and next sentence. /Edit.
Booted manually (as described in the last sentence of post # 16), reinstalled grub, and updated grub. That was it. It looks good.
Notice: I've checked my history and I did not create an entry with efibootmgr the last time; probably it was made by update-grub(?).

For fun, have a look at the efibootmgr output, Boot 0 & 1. I have an SSD (sda) and a HDD (sdb) in the laptop.