27% of paris inhabitants left the city overnight based on phone data from 2 of the 4 french mobile phone networks.

I'm unsure of what the number would be if we added the other two phone operators and the people who wanted to leave but could. But this would probably not amount to "most".

source: https://www.leparisien.fr/paris-75/confinement-plus-de-25000... and https://www.insee.fr/fr/information/4477356