I’m curious about couple of things in your reply, being a professional electrician here in France myself.
You should say that a 2,5mm² circuit for an oven can have maximum 20A disjoncteur. Personally if such a circuit terminates in a 16A socket I only ever fit a 16A disjoncteur. This slightly lower rating also helps with the new calculation for needing a 40A or 63A ID controlling a row of circuits.
Whilst there’s no harm in wiring an individual extractor (by which I assume you mean a cooker hood) back to the board it’s perfectly acceptable to provide a socket for one from a normal socket circuit. I would not connect such a thing to another specialised circuit as you have suggested.
My big question is where you have got the idea that anything that has a water feed needs it’s own circuit? I’ve certainly never come across that in any texts I’ve read, so if you can point me at your source I’d be very grateful.
I agree that some items on your list require their own “circuit specialisé” due to being high load appliances (washing machine, tumble dryer, dish washer, water heater) but fridges (or freezers) do not require such (though they are certainly a good idea, ideally separated from any other différentiel that might switch them off due a fault elsewhere). As for water softeners, I’ve never seen anything specific about them.
Yes, electrical regulations in France have got increasingly complicated over the years. You have to have your wits about you to keep up, hence my concern that I might have missed something…