I sacrificed a Knight in this game but the computer suggests to sacrifice the Rook instead. Can anyone explain me why?
After your knight sacrifice 19...Nxe4 you stay one piece behind.
If you go 19...Rxe4 you only lose an exchange against 2 pawns.
20 Nxe4 Nxe4 and if now 21 Bxg4 Bxg4 22 Qxg4 Nxd2. So the Knight can take a piece back 22...Nxd2, what the rook cannot.
After 20...Nxe4 21.Nxe4 Rxe4 22. Bxg4 Bxg4 23.Qxg4 you are down a piece. After 20...Rxe4 21.Nxe4 Nxe4 22. Bxg4 Bxg4 23.Qxg4 Nxd2 you are only down an exchange, but with two extra pawns there should be compensation.