The achievement asks you to explore the whole map, but after discovering all the points, the achievement was not validated.
After opening a post here and getting no response, I asked the Steam community.
It turns out that the devs changed the way to get this achievement without changing the description.
So currently, it asks you to discover the whole map when in reality the conditions for obtaining it are quite different.
I won’t give the complete solution, but since the implementation of the journeys, the conditions have changed.
So even if you can play this game with your eyes closed, do your thing and you will be successful.
Message for the devs : please modify the description of obtaining this achievement on Steam.
Merci for community Steam :