I wonder how open source works in that framework. I wonder if “we make the device, but use an open source library, we didn’t develop it, but could at least fork and maintain operations if we needed” is acceptable.

No, even worse, it means the EU has some sort of leverage on it or control over the company or entity.

Politics are playing politics. Also, the EU is pretty liberal and US big tech company are lobbying a lot against FOSS.

Politics don't understand free software, and the people who should be teaching it (GAFAM) don't, because it's not in their interest. As a liberal, free software worth nothing. Big tech worth a lot. They don't understand that's about tools and know-how, not about human resources and money.