Thanks, I was looking at "Is on screen" at a property, not like a condition. This method works:
Is this good, or is there a better way ?
"Count" picks all the objects, regardless the conditions before (I tried it before opening this thread)... "PickedCount" counts only the objects that respect the conditions.
My first method doesn't work because the condition "is on-screen" becomes 0/false when there is no on-screen object. An expression like "object.CountOnScreen" would had been useful in this case.