Not french but I did build the RER network in a previous game (version 1.6/1.7). Paris metro might be more of a challenge based on the way station connections/passenger AI works

Is your RER map incompatible with v1.8? (Would it take a lot of time to fix it up and would you be willing to share it?)

It was part of a massive network, it was primarily used to force feed passengers into long distance trains going to Brussels and Germany. I've abandoned that game because of the need to re time everything based on the new braking profiles.

NB: I've just discovered the share.nimbyrails.com sharing site; I though shares we only on this forum, on the reeevant sub-forum. There seems to be amazing work done, such as the "PARIS RER/METRO/TRAM/TRANSILIEN 2022"... Which is labeled "v1.8" ! (How am I even supposed to resist buying this game after seeing this!?)

Is one of them yours?

No

Hi Lentille !
There is at least one :) I am curently working on another part of France, the south-west. I am creating a network based on somewhat the old Compagnie des chemins de fer du midi area, following real network and adding lines that I think could improve the transportation system. My save is not uploaded yet.
Anyway, I strongly advise to you that you buy the game ;)
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Salut Lentille !
Il y en a au moins un ;) Pour ma part je travaille sur un autre secteur géographique, je créé un réseau qui englobe à peu près l'ancienne Compagnie des chemins de fer du midi en me basant sur le réel et sur ce qui je pense pourrais améliorer l'existant. Ma sauvegarde n'est pas encore en ligne, j’attends que le réseau soit un peu plus développé d'abord.
Ce jeu est vraiment excellent, je te le conseille :)