Debian installer preseed fails

[Ceppo <ceppo@oziosi.org>]

Hello.
I'm trying to create a custom install image for Debian 12 preseeding the ISO as
described at [1]. Amongst other things, I want nothing from non-free-firmware,
non-free or contrib to get installed. I therefore set

    d-i hw-detect/load_firmware boolean false
    d-i apt-setup/non-free-firmware boolean false
    d-i apt-setup/non-free boolean false
    d-i apt-setup/contrib boolean false

but package intel-microcode from non-free-firmware always gets automatically
installed. All the other settings I preseed work as expected.
Can someone help me to fix this?
Thanks,

Ceppo


[1] <https://wiki.debian.org/DebianInstaller/Preseed/EditIso>


--
Ceppo