I don't have the option showed by the right red arrow. I choosed the extruder with a right clic (context menu) on the part.
This morning I have made an other test : i have disabled the first extruder in the menu : settings/extruder 1/ disable extruder. And it works.
For information, when i install a new version of Cura , i always keep the previous one, just in case.
I have tried to reinstate the new version and delete the old one, I still don't have the option in the print settings menu on the right, and still the same problème.