Regulation (EU) 2019/945 is the delegated regulation on the product requirements for unmanned aircraft systems. It defines drone classes C0–C6 and the technical requirements of each class — mass, speed, geo-awareness, remote identification and noise levels.
If 2019/947 says how you may fly, 2019/945 says what a compliant drone is. It also places obligations on manufacturers and importers — the class marking on a drone's box is a direct product of this regulation, and it determines which subcategory the drone may be flown in.