Unless a full economy develops under Libra, people will want to convert their Libra to Euros. So you ban the exchanges from operating in your country and force banks to reject any transfers from them. Make using Libra hard enough that most potential users are discouraged, and with low adoption the currency becomes useless.

> Interestingly though, this is exactly what a free country should not do I guess.

I think a free country should be able to put restrictions in place to avoid foreign profit-driven corporations to interfere and manipulate their economy.

France and Germany are not "the Euro" and IIRC can't decide on their own on EU monetary policies. If they were, we wouldn't be far from the colonial era.