The original game uses "SafeDisc" DRM, which Windows 10 and 11 block for security reasons. To get it running, you will likely need a "No-CD" patch to bypass the disc check.
Make sure to install the FS2004 v9.1 Update to fix early bugs and improve performance. Quick Comparison: Retro vs. Modern How to Install and Run Flight Simulator 2004 in Windows 10 The original game uses "SafeDisc" DRM, which Windows
Since Microsoft no longer sells or supports the 2004 version, it has transitioned into "abandonware" territory: The original game uses "SafeDisc" DRM
