What I think worked: Followed JoryDeKort's list of 11 steps, above. I noticed in Activity Monitor that there was still a process with "simulator" in the name, so I thought "let's shut the whole thing down and try again after a fresh reboot". So I rebooted, then (without opening Xcode), ran "update_dyld_sim_shared_cache" again, got the warning, hit Show In Finder. Then I opened Xcode 15 beta 2, got the warning again, hit Cancel, and continued getting a series of prompts and I just kept slamming the Cancel button ... and ... voilà, eventually Xcode stopped showing the dialog prompt, the SBOD (spinning beachball of death/mouse activity indicator) spun around for many seconds as I held my breath (I'm sure that was an important step!) and then ... Xcode just opened my project! I looked in Xcode Settings->Platforms and iOS 17 beta no longer had a Get button, and looked installed. I changed the Run Destination in Xcode to iPhone 14 Pro (previously, of course, no iOS 17 destinations showed up there, so I was very hopeful), I hit Run, and my app magically appeared in an iOS 17 simulator!! Hurray! Thank you Jory!

Jory did most of the work, but I think we got it figured out here: https://developer.apple.com/forums/thread/732324?page=1#756868022

See this: https://developer.apple.com/forums/thread/732324