Demand Priority Rule is neither considering the Item Categories as an Attribute nor to add DFF on UI

For Constrained Supply Planning, the system is not allowing to attach Item Categories as a demand priority attribute. The requirement is to have Rank 1 for A Class Items for Sales Order as Order type. Then Rank 2 for B Class Items for Sales Order as Order type. And then Rank 3 for A Class items for Forecast as Order type. To configure this requirement, Demand Priority Rule is neither considering the Item Categories as an Attribute nor allowing to add a DFF for ABC classification so that if chosen A Class items, the demand priority rule should show the