Tested this on an and brand new macOS box. Happens on not only existing projects, but a brand new project as well.
For whatever reason when I go to add a Blueprint → Pick Parent Class → click All Classes the editor completely freezes, I get the spiny ball of death, and have to force quit the editor.
Are the specs listed above for the mac running ? If you open a Blank Third Person Blueprint Project does this happen every time or randomly? Finally, as a troubleshooting step, try deleting the DerivedDataCache folder from the install folder and restart the Launcher/Editor.
The specs are the same for both machines. I’ve tried deleting the DerivedDataCache folder based on other info I dug up but no change. I’ll give the Third Person project a shot next.
I was able to get around my problem by enabling Show Engine Content in the Content Browser (my goal was to build a GameInstance and SaveGameInstance).
I’ve converted your comment to the answer as workaround for users experiencing a similar issue. I was not able reproduce the issue on the exact model MacBook Pro following these steps:
Create a new Blueprint in the Content Browser as shown below: