Exactly. “You are no fun” means it’s not enjoyable to spend time around/with you. “You are not funny” means you don’t have a good sense of humor. Your jokes don’t make me laugh. You are not witty.

Big difference! You are no fun means that you do not enjoy doing fun things and activities with family or friends. You are not funny means that you do not have a good sense of humor (you don't tell good jokes).