Currently in D365 F&O it's not possible to manage the subcontracting intercompany process.

If you want to internally subcontract an operation in company A and manufacture this operation in company B, the service item in subcontracting purchase order in company A, becomes a service item in the intercompany sales order in the company B.

In company B, it's not possible to connect the service item to a production order for the subcontracted finished item.

Having this will greatly support customers business. Kindly consider this with high priority.