Thanks @SupportiveEntity for suggesting it’s an unusual error on macbook. I noted the lack of other people with same error. I think it boiled down to not having Xcode installed before, but I did have xcode tools, and perhaps that confused unreal engine.
My fix was: homebrew install mas, then: mas install Xcode <you actually use the id, not the word 'Xcode" from the list>, then, accepting the Xcode license agreement.
Once I did all these things, it got past that error, and I got the editor open.
Hope this helps any others who get a similar error on new macbook, and like me, had Xtools installed, but not Xcode editor.