This is the hell with developing in Swift. Need to upgrade some old project for latest iOS? Ok, you need the latest XCode. But ... oops, you need to upgrade Swift language version. Ok, no problem, XCode should be able to do that. But, oops, you need older XCode version to do that. Ok let's download that older one. Oops, older XCode is not compatible with current macOS version. Need machine with older macOS version ...