I just what to know if there’s any ability that allows you to hit Dark-types with Psychic-type moves.
If you're looking for an ability similar to Scrappy that allows Normal And Fighting type moves to hit Ghost types, then the answer is no.
The only way to hit Dark types with a Psychic type move is if you change their type with moves like Soak and Magic Powder. Some Psychic types can learn Magic Powder which changes the opponents type to Psychic. Miracle eye is also a move that allows Psychic types to hit Dark types.
Hope I helped!
No, but if you use the move Miracle Eye, it allows Psychic moves to hit Dark types. This move is unavailable in Gen 8.