In France, the law says the employer must use an email platform that disables communication during non-working hours.

Yes, it exists. Yes, no-one can notify the guy on duty because no-one can send him emails.

Eventually, policies like these lead to “don’t hire employees in France”. At which point, no French employees are even bothered by employers on their free time again...

Ah, you say "don't hire employees in France" but it reads "don't grab slaves in France". If worker's rights are an issue for you, those people in France are better without your "job", thank you very much. There are many many other jobs without near-slavery conditions, luckily.

Yeah, "This guy is great but we will have a hard time contacting him spontaneously after hours so I guess it's back to the hiring pool!"

...is not a sentence that'd be said very often/ever.

No, manage your own life. You work with me, you should know my schedule. And if you don't, consult it in the timetable. Your laziness is no excuse.