I think it should be noted that Prepar3D exists for 12 years now [1] and has been heavily used by flight sim enthusiasts after FSX development was stopped and before MSFS came to the market. It is somewhat unclear were exactly this is used for professional training. The US Air Force apparently uses it for their pilot training [2], and some sort of F-16 simulator seems to exist [3]. I assume their F-35 simulators are also based on Prepar3D.

[1] https://en.wikipedia.org/wiki/Microsoft_Flight_Simulator#Loc...

[2] https://youtu.be/NMLg7THwhAI?t=164

[3] https://www.lockheedmartin.com/content/dam/lockheed-martin/r...