If the objective is "Sovereignty", as clearly stated in the context, then Open Source is potentially a good strategy, but in itself not sufficient. E.g. Switching from Windows Server to RHEL gives you an Open Source initiative, but leaves you (arguably less, but still) dependent on the US.

For Open Source to work "Sovereign" you need to establish an local independent EU maintenance, development and distribution ecosystem for the specific packages that can operate autonomously and independent of upstream.