Right click on the CCX and select “Open With”. If there is an option called “Unified Plugin Installer Agent” then select that and it will run the installer. That is what is suppose to happen when double clicking.
If you don’t see that option then you need to uninstall Creative Cloud and install it again. The “Unified Plugin Installer Agent” is part of Creative Cloud.
If you do see “Unified Plugin Installer Agent” when selecting Open With then you can try settign the OS prefernces to open always with that as it is suppose to do when double clicking. However, in my experience, you may need to reinstal Creative Cloud to make it work by double clicking as it is suppose to.
Adobe has had issues with CCX installers and reinstalling Creative Cloud has been the ultimate fix. It is getting better but these issues still pop up from time to time. Adobe offers no way to manually install files or install in any other way except using a CCX file or uploading the plugin to the Adobe exchange (which I don’t plan to do for SPA).