Let's remember now and then that so-called FOSS licences are derived from an interpretation of american jurisprudence on copyright. These licences uphold intellectual property as a legitimate legal form. In fact they need to do so to function at all.
This is not the same as public domain ownership. FOSS doesn't automatically result in an expansion of the commons. FOSS licences say nothing about the governance of objects either, a FOSS object is not inherently more democratic just because it is FOSS.
So it seems a bit odd to me to state that “A public cloud for the EU, in the public interest and with European values” must be built with FOSS licences. It's unclear to me how it follows from a FOSS license that the resulting product will have public interests at heart. This theory of change is incomplete.
Let's consider for a moment that much of “the american cloud”, much criticized these days, is also built with FOSS.
Trying to emancipate from one techbro's ecosystem by moving to another techbro's ecosystem is not what real change looks like.