As @RayC says, the initial arrival location isn't France, and by EU law they can be sent back to their initial point of EU entry. However the French don't.
The UK is no longer part of the EU, however their embarkcation point is France, so technically all it takes is UK to pass the same law. However the wokeraty would be coughing over their bowl of breakfast Quinoa and smashed avocado on toast if such a thing became reality, yet they'll all say no to offering temporary accommodation to any that land.
The Rwanda initiative had legs, and the numbers of boat people arriving did fall. Yet as soon as the objectors started creating a scene, so the initiative was held up in red tape the numbers were back and increasing.
Ironically the Germans are looking to adopt the Rwandan idea and take advantage of the investment the UK made building the accommodation, schools, hospitals etc to house them.
To stop them it needs a strong deterrent, but with politics so woke, it won't happen.