Laimeduck, I appreciate your situation but was passing on information to the OP in, I hope, offering information regarding his question, from my knowledge and perspective, not to get into a discussion of the rights and wrongs or the ifs and buts of an individual's situation. I also appreciate your personal situation as, certainly with the UK, they keep moving the goalposts, unlike the continent, where at least your designation is for the life of the vehicle. We changed ours from our very much loved but noncompliant Eldiss in 2015 to meet the current, and we thought immediate future, regulations only to find a year later we were no longer compliant!!!
However my experience both approaching Lille and on another occasion Lyon it started with large matrix boards saying, obviously in French and translated by my co-pilot, High Pollution reduce speed to 50kph. The next said Vehicles Crit Air 3 all others leave at next junction. I am not aware of what happens when you leave at the junction as we were compliant. I did observe gantries with cameras covering all lanes after the junction but I am not aware what these were for.
With the Lyon one we did take the diversion as there was an extreme amount of traffic on the road we intended to use and it basically put us onto another Autoroute that circled further out from Lyon with Matrix boards notifying where you should go.
The only thing I would say is if you are alone and only have the grasp of French that I do, it could be difficult!
Bas