I'm in the same boat, iPhone 7 with iOS 15.8.2 and Xcode just keeps 'preparing' the device forever.
This seems to be a chronic problem, I found people reporting the same issue since at least 2014 (eg: https://github.com/ios-control/ios-deploy/issues/73).
Apple really rocks when it comes to making hardware, but when it comes to developer support, it sucks so much that it makes it impossible to believe that Apple is the most valuable company in the world...
tumeo
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