It depends: on the drone, the weather conditions, the lighting conditions, etc. The pilot must be able to recognise the drone and its flight attitude without optical aids. The visual flight rules (VFR) apply - see §21b para. 1 LuftVO.
As a rule, small drones (such as the Phantom) can still be recognised at a distance of 60m to 90m, while larger UAS (such as the Inspire) can be operated at a distance of up to 100m to 130m.
This means that, unlike small models, large drones can still be operated at significantly greater distances. The position of the sun, for example, also plays a major role: if the drone is illuminated from the side in the evening sun, shapes and colours can be easily recognised. If the drone is in front of a white cloud cover, only the grey contours are visible (even brightly flashing LEDs then appear grey). Other factors are darkness, fog and the shape of the drone.
The use of video goggles (virtual reality) does not replace the visual flight rules and is only permitted under certain conditions.