The version of PySide2 pip installs on Mac includes a copy of Designer but Help, Form → View in Python and maybe other commands say they can’t find the programs that implement the commands. It looks like the PySide2 directory structure doesn’t match what that version of Designer expects. So do follow the instructions in Chapter 13 in the book to install Qt and run Designer and all will be well. (Mostly, see “On Mac, don’t move Designer to Applications”.