You could try one of those mini mirrors that go in bird cages, and a rope with a bell on it. We used to get pieces of cuttle fish from the beach for our birds. Maybe they will find that fun and something entertaining

Back then my family used to have a big coup of budgies and all. We never had toys for them as they just never seemed interested. But you can buy those seeded stick things that hang and they chew and peck on it as they please.

Some pets just have no interest in them while others keep busy playing all day. Mirrors are usually goo for a solo budgie. Otherwise extra perches or climbing branches.