The ADW table DW_WRKFRC_ASG_F already has this column (PAY_SYSTEM_STATUS) but it cannot be added to the semantic model.
The "Add column" semantic model action does not include this column, We opened a SR and found out that it is not part of the RPD physical layer and this requires an enhancement request/idea lab.
This column is important to identify if specific assignments are processed in payroll runs