OS Base
Hi. I don't know if this is the right place for this, but I hope it's not entirely wrong.
As far as I can see the goal of this Project is it build a sovereign OS for the EU.
As the base OS you are considering Fedora Kionite. May I ask why specifically that OS? The company behind Fedora is Red Hat, which is a fully US based company (which is currently owned by IBM, also a fully US based company). So while Fedora is open source, the last say still lays with a US company.
Wouldn't it be better to choose an OS, which is based in Europe for this Project? If an immutable OS as the base is intended (which I assume is the case, since your choice is Kionite), OpenSUSE MicroOS (KDE) or OpenSUSE Aeon (Gnome) might be better suited. These Systems are managed by SUSE, which is an EU company (Germany, to be specific).
If upstream commercial Support is required (as per this document https://eu-os.gitlab.io/goals), OpenSUSE does offer this as well. In that case the base OS would be 'SUSE Linux Micro' or 'SUSE Linux Desktop (SLED)' (the former is inmutable, the latter is mutable).