Update (2023-08-30 @ 20:35 UTC): This issue is now resolved.
We are currently investigating an issue affecting PC/MS Store users where beta participants were inadvertently reverted to build 18.104.22.168. If you are enrolled in the SU13 beta and own Microsoft Flight Simulator on PC/MS Store, we recommend you do not launch the sim at this time as you will be prompted to re-download a significant amount of content. We will provide an update when we have more information.
Note: Xbox and Steam users are not affected by this issue. If you are not enrolled in the SU13 beta, this issue does not affect you either.
Thank you for your patience and understanding.