This iPhone is running iOS xx.x which may not be supported by this version of Xcode

This is more or less for me because I keep forgetting where the repository with all of the device support files is and where the device support files should be placed. If you’re here because you need help with this error then follow the short tutorial below:

1. Go to https://github.com/iGhibli/iOS-DeviceSupport/tree/master/DeviceSupport and find the device support files that Xcode claims you’re missing, then download the file.
2. Unzip the file
3. Go to your Applications folder
4. Right-click Xcode and choose “Show Package Contents”
5. Navigate to Contents->Developer->Platforms->iPhoneOS.platform->DeviceSupport
6. Copy and past the folder you extracted from step 1 to this location
7. Restart Xcode

All should be good now.