I am experiencing the same thing even today on Xcode 12.5 (12E262) in every simulator instance - I am gathering the xcrun simctl diagnose output and will file a feedback.

I filed feedback FB9180720 and got a response: Please know that our engineering team has determined that this issue behaves as intended based on the information provided. This is by design. So it looks like this behavior won't ever change.

I'm still not seeing the extension types/templates in Xcode 13 beta 4. Is the answer still to create the extensions manually?

Same issue here. Has anyone figured out a fix or a workaround for this?