When I open SageMath-9.0.app under macOS Catallina (10.15.2), I get an immediate pop-up error window saying, "Jupyter Server failed to start".
The log shows:
┌────────────────────────────────────────────────────────────────────┐ │ SageMath version 9.0, Release Date: 2020-01-01 │ │ Using Python 3.7.3. Type "help()" for help. │ └────────────────────────────────────────────────────────────────────┘ Please wait while the Sage Jupyter Notebook server starts...
However, I can get the Jupyter server to start with an indirect method that was never required in earlier versions of SageMath-x.x.app, namely: In Finder, Show package contents for SageMath-9.0.app. Navigate in Finder to Contents/MacOS. Double-click Sage. That both starts the server and opens the expected client window in Safari, from which I can open and evaluate cells in an existing notebook or create a new SageMath 9.0 notebook.
So something that used to be "hooked up" between the SageMath-x.x.app and the command to start the jupyter server has been broken with 9.0.
