iOS 15.6 beta / iPad OS 15.6 beta に上げたら Xcode と繋げれなくて悩んでたんですけど、Xcode 13.4 は未対応なんですね https://developer.apple.com/documentation/ios-ipados-release-notes/ios-ipados-15_6-release-notes

Xcode 13.4 is unable to prepare iOS 15.6 beta devices for development (93452791) Workaround: Use Xcode 13.3.1.