I worked on my project for a while on my laptop, which is running Xcode 13. Now I cannot open it on my High Sierra desktop running XCode 10.1.
The alert says to adjust the project format in a compatible version of XCode, but the project format is already XCode 3.2.
Why won't it open? It opened fine before I worked on it on the laptop.
Are you sure the project format is still Xcode 3.2 after working on the project in Xcode 13?
Xcode 13 changed the project file format. Working on your project in Xcode 13 may have changed the project format to Xcode 13 so it won't open in Xcode 10. Other people ran into a similar issue, and the fix was to open the project in Xcode 13 and set the project format to an earlier Xcode version.