Psychic does ×½ to Steel

Generations VI to IX, single types. The other way round, Steel against Psychic, is ×1.

102 Psychic and 65 Steel species among the 1025 this site covers.

Attacker, Psychic Mewtwo sprite

Mewtwo #0150

damage×½Generations VI to IX

Defender, Rock and Steel Stakataka sprite

Steel did not exist in Generation I, so Psychic against Steel has no value there.

Strongest Psychic attackers

Mewtwo leads Psychic at Sp. Atk 154

Sturdiest Steel defenders

Dual types that change the answer