> France at least would shield NATO and EU with the nuclear umbrella even if the US leaves NATO

This is absolutely not the case. The French nuclear arsenal is controlled separately to the joint NATO command and the French have traditionally made it very clear it is for the protection of France, not NATO. Indeed France left NATO for years partly over this and only rejoined in 2009.

Macron has opened discussions about a "pan-Europe" nuclear shield, but be very clear: if Russia was to use battlefield nuclear weapons in say Poland, there is no expectation that France would respond. There is an expectation that NATO would respond (or there was last year.. who knows if NATO is reliable now?)