In which situation does ATC not provide traffic separation?

ATC does not provide traffic separation under VFR-on-top conditions because, in this scenario, pilots are flying VFR (Visual Flight Rules) at an altitude that is above an overcast cloud layer. Although these pilots are operating under VFR, they are still responsible for their own navigation and situational awareness, which includes maintaining visual separation from other aircraft. When pilots are VFR-on-top, they are not being monitored in the same manner as aircraft under IFR (Instrument Flight Rules) and therefore ATC does not have a mandate to provide separation services. This allows them to operate more independently, unlike in controlled airspace where ATC actively manages traffic or at night under VFR where visibility may be less and increased separation is often necessary. In IMC (Instrument Meteorological Conditions), however, ATC does provide traffic separation due to the lack of visual cues and the necessity for IFR operations.