Adobe Air, a tool on which the Scratch 2.0 offline editor was built, does not work on any version of MacOS newer than version 10.15 (Catalina). This is out of our control, as the tool was developed by another company. It is unclear if Adobe Air will ever be upgraded so that it will work on Catalina.  

In preparation for the loss of support of technologies that Scratch 2.0, including the offline editor, was built on, we developed Scratch 3.0 and Scratch Desktop. We recommend that you start using Scratch 3.0, which you can get at