Not a big stats guy when it comes to defense, but this article confirms what I remember from his days with the Jazz.
https://theathletic.com/3634665/2022/09/27/cavs-donovan-mitchell-defense/
"While the Cavs have the size and length in their frontcourt, there are questions surrounding their backcourt, particularly in newcomer Mitchell. Last season, the Jazz gave up 105.2 points per 100 possessions with Mitchell on the bench and 111.7 points with him on the floor,
per NBA Stats. He struggled in the playoffs to defend well, as the Jazz gave up 115.3 points per 100 possessions with him on the floor, versus 104.5 points with Mitchell on the bench over six games in their first-round playoff series against the
Dallas Mavericks.
Mitchell was also rated a bottom-20 defender in the
NBA by
FiveThirtyEight’s RAPTOR. He had a defensive RAPTOR of -2.7, which means the Jazz’ defensive performance fell by 2.7 points per 100 possessions while Mitchell was on the court."