There are some nuances to be aware which affect whether or not the Process Form will be visible in the selectable list:

• The form must have an Active Version.
• The form must not already be assigned to another Object Name. i.e. Once it's linked to a Resource Object, the Process Form is then permanently linked to that specific Resource Object.
• Once assigned, it cannot be removed from this Process Definition. (for example if you wanted to change which Process Form this Process Definition is responsible for.)