I read somewhere online that if they don't go near an item of food then to take out what they normally eat, and soon they will get curios and go and try it. Is this something you recommend?
Perhaps it may be presentation. A small budgie may not want the apple because it's presented in such huge pieces. Cutting them down to very small, bite size pieces for your budgie to enjoy might make him enjoy it a little more. You can also feed him a variety of other fruits and veggies, as well as cooked legumes and grains. Check out my recent thread about my batches of bird CHOP I make for my two birds
The CHOP Chronicles!
Diet is actually very important and may be a cause of some issues you are having with your budgie. A diet high in seeds is not good, as well as too much fruit, which has a lot of sugar, can be harmful. Try mixing it up with different things and his health may improve. Of course, a certified avian vet will be able to determine what is making him act different.