UPDATE: I solved this by downloading 2020.3.3 (Apple Silicon version) again from jetbrains.com and installed manually. The broken version is the version managed by Toolbox.
(I know I'm using an old version! It is because it's the only version I have my Sencha Ext JS plug-in working in!)
After upgrading macOS 13.5.1 to 13.6, PHPStorm 2020.3.3 is no longer launching, just beachball spinning.
Is there anything I can do to fix this situation?