Please note that this section relates only to regions, countries and continents, not cities or particular airports.
Microsoft offers with the new Microsoft Flight Simulator 2020 sceneries of incredible quality and the performance is also excellent. Microsoft has a general store called Marketplace where you can find a huge number of additions according to your taste and needs. The company regularly updates the flight simulator and adds, free of charge, new aircrafts, challenges, and other significant improvements to the game.
Another very good company for flight simulation is ORBX . You have the possibility to improve the visual aspect of the simulation by progressively adding layers that offer a higher definition of the territory. Buying a particular region means that many 3D buildings will be included, adding to the realism.
There is also an excellent service. If you have a problem with the installation or anything else, you just post your question on their technical forum and somebody will work on the issue. The company offers the possibility of free downloads for an unlimited period, which includes a full country like Iceland.
For those of you who are specifically interested in France, there is: France VFR
For X-Plane:
There are, among others, FS Elite et X-Plane.Org