On a whim, decided to reboot and alas I can now create an iPhone Duo simulator. Thanks for your help on this!

A good thought, but no luck. Re-installed Xcode 27.1 beta, clicked "Update" to get the iOS 27.1 beta platform. In Device Hub (verified it's version 27.1), the OS version popup only ever includes "iOS 26.5" back to "iOS 18.0". Clicking on "Add Platforms in Xcode..." then only lists older SDKs. At this point, I can only assume this is some incompatibility with my Mac (M2 Ultra Mac Studio running macOS 27.0) that is leading to something getting messed up during installation of the tools.

Thank you, OlenaS. I will add that note to my bug report.

Yea no doubt it would have been better if Apple would have at least updated the bug report with notes. I do see a "Potential fix identified - in Xcode 14" on my bug report now, but that's a bit useless. Which version? Beta 3? later? Also no notes whatsoever. On a related note, Apple has not updated any of my bug reports with notes going back to 2019. I miss the years when they used to do that.