D&D Chronicles of Mystara (side-scrolling co-op) I think is 4-player

Cuphead - 2 player

A Hat In Time - 2 player

Streets of Rogue - up to 4 players

Vampire Survivors - I think 2 player for local co-op?

Most of the old Telltale games have co-op in the form of voting for responses

Binding of Isaac: Rebirth has full co-op now, I think up to 4 player. You may need the DLC for the best co-op experience

Crypt of The Necrodancer has solid couch co-op

Baldur’s Gate 3 has a full split-screen 2-player couch co-op mode. Both players need to use a controller. Works great.