Hi,
I had the problem, in my case for version 14.7. And my surprise is that it was not available on GitHub,
I managed to fix the problem by doing this:
Search and Download the required version of required os, or like in my case the closest available version of required os from GitHub in my case it was 14.6.
Add downloaded iOS version (14.6) to the device support file inside the Xcode app in path contents/Developer/platform/iPhoneOS.platform/DeviceSupport (if you found the required version of the OS, the solution ends here).
Try using iOS 14.6 device support files, just name it "14.7".
I was able to run on iOS 14.7 using iOS 14.6 device support files on Xcode 12.4.
ty