"We will do the activities we planned."
Translation:Nous ferons les activités que nous avons prévues.
I have the same question. I'm wondering if it is because planifier is an anglicism or perhaps not standard French? Even if an anglicism or not standard, it seems to be used often enough. Or maybe the choice of verbs distinguishes between different types of planning? I really don't know. Maybe it is just an oddity of Duo? If anybody has any insights, they would be appreciated.