First, add a new Activity Type for "Task":

Note: You can setup the Activity Type the way you like, I have just shown here the minimum you need - the NAME and ICON.  Take a note of the ID from the URL:

Next, add a new field to the Activities model to store the Project, which will be needed:

Next, add the new field to the Popup Form View, and make it required and visible only when needed (here is where you need the ID of the Task Activity): 

Code:

 <field name="activity_type_id" position="after">
            <field name="x_project" 
                   attrs="{'invisible':['|',('activity_type_id','=',False),('activity_type_id','!=',21)], 
                           'required':[('activity_type_id','=',21)]}" 
                   options="{'no_create': True, 'no_open': True}"/>
</field>

Next, create an Automated Action to listen for the creation of the Activity and create the Task:

This gives you something like this: