Will a unique facility identifier (such as a GLN) be required only for listing economic operators or manufacturing partners for the finished good?

The usage of GLN has been clarified by the GS1 AIDC provisional application standard for DPP, available HERE.

Economic operators

Economic operators are the manufacturer/brand owner, the authorised representative of the 

manufacturer/brand owner, the importer, the distributor, the dealer and the fulfilment service provider dealing with products that are subject to the ESPR. The economic operator responsible for assigning the GTIN is the GTIN allocator and for creating the DPP is the brand owner. The economic operator responsible for making the DPP data available is the one placing the product on the market, e.g. the brand owner/manufacturer or its authorised representative when located within the EU, or the importer. Dealers must ensure that customers have access to relevant information accompanying the product required by EU delegated Acts including in cases of distance selling. The ISO/IEC 15459 compliant unique operator identifier in the GS1 system SHALL be the GLN.

Facilities 

Facilities are locations or buildings involved in the value chain of a product. For the DPP, the identifier is required for the facility where the product was produced. The ISO/IEC 15459 compliant unique facility identifier in the GS1 system SHALL be the GLN.