It's quite common for kids to eat more earlier in the day and not so much later on. If he isn't hungry he will still eat something nice like dessert (I would too).
I wouldn't try to force or use the TV/toys etc offer the meal and he either eats or doesn't. If he is hungry later offer the same meal back or something like a cracker or bread stick.
I had a phase were I dramatically reduced the amount of fruit I allowed DS to have because I really felt it was impacting on him getting a balanced diet. he wasn't particularly happy about it for a few days, I would comfort him with hugs and soothing words, explain that it is my job to ensure he has a balance diet and offer him something else when he asked for food. But at another time I've done the same as pp and given fruit (a small amount) at the beginning of a meal or with a meal as it seems to get his appetite going, then he'll eat the main meal.
Another thing I tried quite recently was changing breakfast. My DS wasn't good at eating protein and trying to get protein in at lunch or dinner is so hard when the appetite is naturally lower anyway. So I shifted protein to breakfast with 100% success on day one. I gave a full sausage or a full egg every day for a week and it was never refused, he ate the lot. He's never had so much protein in his life. We now switch it around sometimes protein breakfast sometimes carbs/cereal.
So if you are worried about overall balance of diet, as odd as it might sound maybe switch around the meals, veg and protein at breakfast and keep the cereal for dinner? It isn't going to be for ever.
Slightly OT but my boy just did his first no nap day too and it is a massive comfort for me to know I can feed him anything for breakfast (doesn't need to be a 'typical' breakfast) because he might have little or no appetite at dinner or miss altogether because of tiredness before EBT.