Check out this recent thread
re walking from Paris to Santiago.
From a Belgian site check out this page
and aim for Massy the first day. Massy is 18 km. from Notre Dame cathedral in Paris. The Belgian site offers invaluable info re walking/stopping from Paris south. Do explore the other links on that site.
is most useful for walking to Massy.
Also here is a thread
from a pilgrim who walked from Paris in 2022.
What Pafayac mentions in post #3 above is the donativo Chaîne d'Hospitalité Locale
.Those who offer pilgrims such hospitality do so for the pleasure of meeting/greeting/helping pilgrims.
During past easier years my husband and I ran a b&b/pilgrim house in our farmhouse facing the Marne river as part of the local Chaine. My first pilgrim shell hung at the door marking it as a pilgrim place.
Good luck with your plans and Bon chemin.