Flight Simulator is a Microsoft app. It doesn't work on Windows Arm. If Microsoft is serious about Arm as a platform, the least they can do is make sure one of their most iconic game titles works on Windows Arm.
MSFS is made by Asobo, who aren't actually a Microsoft-owned studio. The name is just tradition at this point.
It does not work on Windows ARM because it is a game that was develop for a regular Windows and consoles. It is not the "app".