On April 26, it was reported that Shohei Ohtani of the Angels was the first player to start a game while also leading the major leagues in home runs since Babe Ruth did it on June 13, 1921.
I saw something yesterday that implied this might not be completely accurate, so I checked it out. After June 1921, Ruth pitched in three more games for the Yankees: two starts and one relief stint.
October 1, 1921: Ruth pitched four innings of relief in the second game of a doubleheader, the penultimate game of the season.