Throne room, rooms for the Lord, maybe even rooms for the Lady, if it’s big enough. They’d likely have formal and informal sitting rooms, studies, offices, personal libraries, private dining rooms, etc.
You also can’t have a keep without a vault/treasure room!
And, there’d probably also be a place for clerks, tax assessors, and scribes to work.
A keep is often responsible for the administration of a large domain, so it needs the capability to manage all that entails