Drone operators are obliged to register as soon as they operate drones weighing 250g or more or with the possibility of recording personal data (i.e. a camera). The electronic registration number (e-ID) issued as a result must be attached to your drone.
You are only registered as a drone pilot once you have received an EU drone licence. You then have a remote pilot number (RP-ID, Remote Pilot ID). This is possible regardless of operator registration.