I am glad that it is working using the latest version of AppStudio for Desktop.
Yes, the Cloud Make environment used is dependent on the version of the AppStudio Desktop, the Cloud Make is being called from.
In your case, AppStudio 2.1 Cloud Make environment is using Xcode 8 to build the IPA file for iOS, that is no longer supported by Apple. Watch out for a blog that is coming out very soon regarding this.