After hours and hours, I managed to distribute it to TestFlight, BUT, the application directly crashes when I run it:
Library Not loaded => code signature invalid.
So I started all over.
I have created a new certificate - Mac App Distribution
I have created a new Provisioning Profile - Mac App
At XCode level, I have unselected the "Automatically manage signing" and when I am trying to import the Provisioning Profile, XCode says that the signing certificate could not be found...