Welcome here!
I would suggest you gradually begin to change him to a healthier pellet. Seeds, nuts, corn, cereal pieces, colored bits, etc are considered bunny junk food. That is why he’s eating those and leaving the good, healthy pellets behind. It’s recommended that adult bunnies get a limited amount of plain timothy pellets (about 1/8-1/4 cup per day per 5 pounds of bunny). They don’t actually NEED pellets tho. They are good to feed in limited amounts b/c they can fill in the nutritional gaps left by the hay and veggies, but they are not necessary and some members give either no pellets, or a very minimal amount (like a teaspoon a day).
While you switch over to a healthier pellet, he may boycott them. Continue to offer them tho and if he wants pellets he will eat them. As long as he continues to get unlimited timothy hay and a daily supply of veggies, he will not go hungry.
For more info on diet, there is a diet section under “bunny info” at the top of the page…