The feature to change the playback rate only applies to content owned by the user, such as songs purchased on the iTunes Store. So, help me understand: if I record tracks of my own music, composed and played by me, recorded using software I wrote, I can't change the playback rate?

The process changed in Xcode 13, and there are tips in the release notes. https://developer.apple.com/documentation/xcode-release-notes/xcode-13-release-notes

What's the crashing thread's backtrace?

Anyone who knows can't tell you. Further, just because something is planned doesn't mean the feature makes it in the final; also, some things make it in that even Apple engineers not directly working on it know about. Source: am former Apple engineer.

Radar was also the name of the app Apple engineers used internally as well as the bug database. So it was an overloaded term. So bugreport.apple.com was an external way to report into radar, it just didn't have a full view of a bug. (Source: was a bug screener at Apple for several years and lived in the Radar app all day.) These days, they now have a better front end for it, I understand.