Portal 2 on Steam adds split-screen to co-op mode, Big Picture support - Polygon
Portal 2: Reflection and Cooperation - Médiation thérapeutique avec les Jeux Vidéo
Uhh wtf? What's happening here? (Portal Reloaded coop in split screen, as I can't find ppl. btw it's so damn confusing, and I've played the whole singleplayer campaign...) : r/Portal
Portal 2 PC - local co-op (splitscreen) gameplay - YouTube
Portal 2 PC Split-Screen Tutorial with Controller + Keyboard, Mouse - YouTube
8 Best Split Screen games on Steam as of 2023 - Slant
Portal 2 PC finally gets split-screen co-op | Eurogamer.net