Thank you Kevin!
It works!
That was so frustrating not able to open Sigil on my Mac because Apple wants to manipulate the market, it's understandable not wanting to let users install malware on Apple systems that can open a s**t storm in a IOS System. But Sigil it's been around for a long time about a decade since I started using it.
Anyway, just like Kevin explained, just right click on the icon to open, twice and that should recognize the app, here is the link Kevin sent me in case any other simpatico would like to read the reason why Apple doesn't want you to use the app.
Good luck!
David
https://github.com/Sigil-Ebook/Sigil/issues/588