So, you're like the old me, a dictator who is going to be obeyed regardless of the consequences to the child.
He's not going to conform to your rules, he's going to go hungry day after day after day and then end up sick and it will be your fault. It was my fault when it happened at our house. That's when I realized I was making really bad decisions about food and meal time. I decided to loosen up and have a happier life especially at meal times.
There has to be a happier area where you can get some of what you want and he gets some of what he wants.
The more YOU focus on is conforming to your dictates the more he's going to dig in his heals.
SO let's say he only wants mac and cheese day after day after day after day. You can hid yellow veggies in it. Get the recipe book about hiding foods in kids food. I can't remember what it's called.
Will he eat pasta? With sauce? You can hide beets and carrots and onions and more in spaghetti sauce if you do it in a minimal way so they don't taste it.
There are ways to get what you want without having a war about it and trying to force a 3 year old to conform. He needs to grow up having a voice too. He doesn't get to have one about big things but he should be able to make choices about small things. This is how he learns to make bigger decisions later on.
When you cook your meal make him something that he loves then add what you love to the meal. When you take a bite of the food you like make sounds and say how yummy it is. Don't make him take any or ask him to try it. Just make it sound like the best thing that has ever been in your mouth.
He'll be interested at some point, when the pressure to try foods he doesn't want to try is over and does not exist anymore. The less pressure you put on him the more willing he'll be to try new things. My granddaughter was 8 before she started trying new foods. She eats a lot more things now.
All I can say is that making a stand and trying to force the kids to eat foods they don't want to eat is not something they will respond to. Letting them have more freedom and they'll start to relax and be more interested in trying new things.