Emily and I figured this one out. You install XAMPPP on a Mac. You start it, and Apache works. You can go to http://192... in a browser, and see stuff.
However, when you try to start phpMyAdmin, you get a permission denied error. ARGH!
The fix for Emily's computer was at https://dev.to/josiemhardy/how-to-fix-error-403-forbidden-access-new-xampp-security-concept-on-macbook-n2k.