I didn’t find the cause of the problem but to make it work I decided to do @Sven’s tutorial in a new one:
1. clone and setup your own minimal template
dom0 terminal: qvm-clone debian-12-minimal d12m-mullvad
2. run all update on d12m-mullvad
dom0 terminal: qvm-run --pass-io -u root d12m-mullvad "apt update && apt full-upgrade -y"
3. run on dom0 terminal
qvm-run --pass-io -u root d12m-mullvad "apt install --no-install-recommends qubes-core-agent-networking qubes-core-agent-nautilus nautilus zenity gnome-keyring policykit-1 libblockdev-crypto2 pulseaudio-qubes firefox-esr -y && poweroff"
if you want to know why each line: Debian-10-minimal Configuration - #19 by Sven
4 if you want a sudo without password in your qubes, run this :
dom0 terminal: qvm-run --pass-io -u root d12m-mullvad "apt install --no-install-recommends qubes-core-agent-passwordless-root -y"
From then on I followed @den1ed tutorial
from point number 5 to the end.
tutorial @Sven: Debian-10-minimal Configuration - #12 by Sven