[Skybird]

From their Q&A:


Q: Is Microsoft Flight Simulator going to be released on Steam or the Epic Store?
A: Microsoft Flight Simulator is available on Steam. We have no news to share regarding additional versions, but our goal is to have Microsoft Flight Simulator available on as many platforms as possible.
Q: Is there any differences between the Steam and Microsoft Store version?
A: There is no difference. The sim shares the same multiplayer world and services.
Q: Will people that have the sim on Steam be able to play together with people from Microsoft Store?
A: Yes, the sim shares the same multiplayer world, content and services. However, if you purchase through steam, you will not be able to use the Xbox Play Anywhere functionality (PC Windows 10 and Console).
Q: Are achievements cross-platform?
A: Achievements are not cross-platform. If you unlock achievements on Xbox Live, they won't unlock on steam and vice-versa.
Q: Will people that have the sim on Steam be able to play together with people from Microsoft Store?
A: Yes, the sim shares the same multiplayer world, content and services. However, if you purchase through steam, you will not be able to use the Xbox Play Anywhere functionality (PC Windows 10 and Console).
Q: Is license sharing allowed on PC?
A: No, there is no license sharing. It requires explicit authentication per session.