Notre Dame, page-5

LJ you are totally correct.
“Due to France’s laws regarding secularization, the French government owns all churches built before 1905, including Notre-Dame.
“The government lets the Archdiocese of Paris use the building for free, and will continue to do so in perpetuity. The Archdiocese of Paris is responsible for the upkeep of the church, as well as for paying employees.”

Administrative arrangement only. To all intents and purposes Notre Dame Cathedral is part of the Catholic Church which administers and is responsible for everything to do with this church. There is no way that the French Government would be able to sell this building, hand it over to a different organisation or change its use.

As the nominal owner then, the French Government should be responsible for restoration.