Picked this up for £6 for a nostalgic Silent Assassin run and the Sniper Challenge code worked! Backward compatible on Series X. Figured they would have expired by now? : r/HiTMAN
Hitman 2 - Microsoft Xbox One New Sealed 883929639564 | eBay
Hitman 2: Silent Assassin | Hitman Wiki | Fandom
Xbox backwards compatibility list, with all Xbox 360 games and original Xbox games playable on Xbox One, Xbox Series X | Eurogamer.net