This is like saying that the latest Doom "has been around since 1993".
FS2020 was developed by the French company Asobo.
https://www.asobostudio.com/games/microsoft-flight-simulator
yes I know. It does not mean that they disregarded the whole history of 40 years of FS when designing the game did they ?
[1] https://imgur.com/a/KnP1NKl
[2] https://microsoft-flight-simulator.fandom.com/wiki/Orbit_Air...
The visual "game engine" is from Asobo, though.
It's certainly a more ambitious engine upgrade of the engine than p3d or fsw, even excluding the cloud scenery stuff, but "write a flight sim from scratch" is a task on par with "write a Web browser from scratch".
Yes, most of this forum could write a IE3 or Netscape 2 or Lynx clone in a long but manageable amount of time, but if you want to catch up to Chrome/Firefox/Safari, good luck.
[1]: https://www.nexusmods.com/microsoftflightsimulator/mods/117
If you conveniently ignore the fact that fs has been around since the 80s.