In reality, the white screen border is not fully displayed, it begins at the bottom of the screen as an animation then stops rapidly and it is never fully displayed.
So I've made some more tests and I managed to make it work by enabling the "Screen text analysis" option in Android assistant settings.
In this case, the border is fully displayed and the Automate dialog asking for a flow appears (as I cleared the dialog defaults) and the flow starts correctly.
But if I disable this option, it doesn't work anymore.
As you can imagine, I prefer disabling this option...
I hope this will lead you on the way for insvestigating more precisely.
Thanks.
Luc