Still a heck of a lot more hassle
Why?
Claiming that trains are "green" is tricky due to the huge amount of concrete, steel, etc. involved, although electricity in France is quite green due to lots of nuclear plants.
Peter47 there is a train station directly at CDG, enabling mixed plane / train journeys which really is the way things should be. Vienna sorted this out a few years ago too. London sadly still a backwater where one must trundle along in the Tube for ages to get to a train station.
The SNCF train booking site oui.sncf offers diesel-powered buses and petrol-powered car shares too, which are often cheaper than trains (although presumably less civilized, I have yet to try).
Saturation on the Lignes Grand Vitesse was a problem pre-Covid leading to 800m long pairs of double-decker trains every 2 mins, whereas still plenty of sky available.
Not sure that banning a rather small number of flights operated by CRJs and such will suddenly make a huge difference to mother Earth when China is still opening a new coal fired power station every two weeks. My $0.02, I think hydrogen or electric (or both) aircraft are the future for short flights.