Hello
Your system behavior is correct. The definition of raw material is a material that can only be supplied externally, therefore, it should not be possible to create a production order for this material type.
It means that you cannot create the tab work scheduling for this material type. In addition, the procurement type is always "F - External procurement" and it cannot be changed.
If you need to create a production order for this material, it means that it is a semi-finished material (HALB) instead of a raw material.
Regards
Caetano