We rescued a 35-year-old macaw several months ago whose elderly owner mostly fed him people food along with a seed mix. He's still pretty picky and gets tired of things quickly, but now he eats pellets and chop reliably.
We had the most luck with roudybush California blend. He doesn't absolutely love pellets, but at least he'll eat those. His chop can be hit or miss. We just keep trying different things to see what takes. He doesn't particularly like green vegetables, either, but he happily eats sweet potato and bell pepper (we've been pushing things with vitamin a because our vet suggested it), and he at least tries fruit and chop (he likes apples and bananas but we don't give him those often because of the sugar). We've had some success with sprouts with our other birds, so that also may be worth a try. Also try different textures; we thought the big guy would like his vegetables in chunks because our other south American birds do, but it turns out that he prefers finer chop like our small birds. Good luck! Diet conversion can be a slog.