iPhone is not available. Please reconnect the device. / iOS 14.2 - Xcode 12.1
Update: Xcode 12.2, with support for iOS 14.2, is now available on the AppStore. If you find this problem with a newer version of iOS and Xcode, the answer is still the same, you can (probably) download the beta for the next Xcode version from the Apple Developer website, you can wait for the AppStore version to be updated, or you can (probably) find the symbols for the new iOS version and copy them to your current Xcode installation.
Original answer. Applies to Xcode 12.1 and iOS 14.2
The latest version of Xcode in the AppStore doesn’t include support for 14.2. You can download a beta of the next version from the Apple Developer website that supports 14.2, or wait for the AppStore version to be updated.
Go to my Github repo iOS 14.2 Device Support File and download 14.2.zip file directly and after unzip it
And just copy and paste unzipped folder by path:
Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/DeviceSupport/Restart the Xcode
That's all. You can build and go on your project.
If you need a visual solution, check out this answer: https://stackoverflow.com/a/64854525
Why we have done these steps?: Because Xcode 12.1 doesn’t include support for 14.2 so we implemented its device support files for 14.2.
https://developer.apple.com/documentation/xcode-release-notes/xcode-12_1-release-notes