In September 2022 19 year old Hans Niemann beat Magnus Carlsen in the Sinquefield Cup.
On the 19th January 2023 18 year old Nodirbek Abdusattorov beat Magnus Carlsen in the Tata Steel tournament.
Is Abdusattorov the youngest player to beat a reigning world champion in a classical (i.e. not rapid or blitz) over-the-board game?