Again/repeat: check out the RES free local TER trains-that bring you into the town itself and not some sugarbeet park&ride stop without sometimes even connect bus.
There is a continuous ´problem´ with RES con the many FR TGV (and the apparent insistence led out by all these planners to stubborn or unknowing rail-newbees): MOST (in fact not all, or one could say the quota = 0) TGV trains offer only a very few pass-holder seats for 10€. IF this quotum is fully taken (and it may be that booking 4 persons means f.e. that 2 could be in and 2 out) then SNCF is said to offer 20€ seats as long as there are any spare seats. NOW this EU/IR-app has been many times mentioned as not being able to handle THESE 20€ places.
I really do not quite understand that immense fear of those newbees for REServ 2 month ahead. MOst likely as a tipical tourist you stay the odd day in Nice or aorund (Cannes? Monte Carlo anyone?) then go to a SNCF counter, show pass and ask for them to do it. Chances the 10€ seats are gone are close to 100% then-but apparently already now and chances to find the 20€ seats are like 99,99%
Chances that the always very unhappy jolly FRench SNCF workers lay on yet another strike are in fact higher as finding cheap seats