where does the system check master data selection settings during the creation of planned orders...

The system checks the master data selection settings during the creation of planned orders and production orders in the following places:

In the bill of material (BOM), the system checks the selection ID, which determines which alternative BOM is selected for the material. The selection ID can be maintained in the material master or in the production version.

In the routing, the system checks the selection ID, which determines which alternative routing is selected for the material. The selection ID can be maintained in the material master or in the production version.

In the production version, the system checks the validity period, the lot size, and the selection profile, which determine whether the production version is valid and applicable for the material. The production version combines the BOM and the routing for a material and can be maintained in the material master or in the production version master data. References: SAP S/4HANA Manufacturing for Planning & Scheduling - Implementation Guide, page 16; [SAP S/4HANA Production Planning and Manufacturing Certification Guide], page 75.