In macOS Catalina and above, Apple has placed significant restrictions on what installers will run without receiving a warning message. This message indicates that Apple cannot check the installer for malicious content. This will likely occur on many programs not downloaded from the Apple App store, and not related to any changes that we have made in our programs or in our installers.
In order to run the installer, double click on the Scaffold DMG file. When the dialog box opens right click or control click on the installer app and select Open. A dialog box will open with the same warning about the installer app not being checked for malicious content. Select Open again and proceed through the installer as normal.
In newer versions of macOS, it might be necessary double click the DMG, then choose Show in Finder, then double click again to re-mount the DMG. At this point, the option to Open will be available and installation can continue.
2023-03-28 This has been tested through Ventura (macOS 13.3)