Carthage is currently not working with Xcode 12. As a workaround a wrapper script has been proposed (see https://gist.github.com/skymobilebuilds/61f4a95bd62a3db36b52719aeab7e0d5). Until the issue is fixed and Carthage can built again with Xcode 12, the wrapper must be used instead of the direct `carthage` command.