Metros with OVL are actually pretty common.
Budapest M1, Barcelona Metro (including FGC S lines), Madrid Metro, Bilbao Metro, Palma de Mallorca Metro, Valencia Metro, Rome Metro, Naples Metro, Catania Metro, Genoa Metro, Lausanne Metro, Tyne and Wear Metro, Vienna Metro U6, Hong Kong MTR, São Paulo Metro Line 4 and Line 5, Tokyo Tozai Line, Chennai Metro, Dehli Metro, Shanghai Metro (excluding Lines 16, 17 and Pujiang).....
I could go on, but Asia is so full of Metro systems, I can't be bothered.
Even some.... newer systems like London's Crossrail Elizabeth Line will have overhead electrification throughout the underground sections of the city. That's not forgetting the underground sections of the Thameslink, which use overhead electrification before joining into the Southern Rail network and switching to 3rd Rail. Then there's the numerous tunnels for things like the RER in Paris, the S-Bahn in Munich and in Leipzig. Berlin's North-South "Ferntunnel" which goes via Berlin Hbf and Potsdamer Platz, and numerous other underground rail lines, either for rapid transit, regional rail or long distance and high speed rail which use new overhead line technologies to enable mainline spec trains to operate in basically metro conditions.
Plus, there's a safety benefit to overhead line in a metro tunnel. If people have to evacuate the train, or someone falls onto the tracks, there's no 3rd rail which will electricute and kill people.