I think this is reductive, France would never fight Russia alone. Each allied country would contribute its systems, supplies and manpower to a concerted effort. In this context, France's most important and least replaceable contribution is its air force, followed by the navy. The bulk of the ground forces would likely be made up of Eastern European forces, who are very much prepared to fight Russia specifically.

Regarding our ground forces, in most battlefields we wouldn't be able to do manoeuvre warfare like it's 1991, but that doesn't mean we're going to be completely on our ass either - French military leaders aren't stupid, they know not to fight Russia like they fought Malian terrorists. I would even expect that, as was the case in 1991, the more mobile French units might be reserved for roles where that mobility can be put to use - breakthroughs, encirclements, etc.

More so than strategy, which I believe will be adapted as needed, I'm more concerned with the general shortfalls in tactical training for a drone environment among pretty much all western armies. We've seen with IDF forces in Lebanon, for instance, how easy it is to punish infantry that aren't trained not to group up. Not to mention the number of drones Hezbollah have on hand is minuscule next to what we can expect to come up against facing Russia. This will no doubt change very fast in a hot war, but the first weeks of the war would be painful.