In the Gen 3 Prius in the US, the same sensor handles both functions. The A/C always uses it, and in models that did not come with auto headlights, some people complete the circuit and enjoy that feature as well. But I don't know if that was the same for Gen 2, and I don't know if it was the same in Greece. I also assume we're talking about the small domed sensor on the left. The larger crater to the right of it? No idea what that's about.
After some Internet search found it as solar sensor. https://www.megazip.net/zapchasti-dlya-avtomobilej/toyota/prius-38345/nhw20-57118/nhw20l-aheebw-937796/heating-air-conditioning-control-air-duct-18053866 I don't see Gen2 with auto headlights here in Greece. Come as standard from Gen3 and later.