Update :
after trying many different options, I found a way of making it work :
If I turn off my audio interface and start Ireal Pro, it will show the built-in outputs .... I then start my audio interface and select it back in the OS System Preferences , then I can select my interface in Ireal Pro ...
Not very convenient but at least it works ... :-)
I'm still wondering if that is a bug or if I'm missing something ?

Thanks