Have to be patient and think positive alright.It's good that your son is eating.Keep encouraging him to eat meats or veggies, by decorating the colourful veggies or put the food in colourful kids plates and cups.Meanwhile check with ur doctor.There're supplements for children to meet the daily nutrients.
same with my daughter until now she is almost 4YO. she start picky when reach 2Yo candies chocolate triger to be picky eater. my hub give all those to her🥲 start give her vit and cook wht she like now she eat well but ya she still cannot eat chicken even chicken nugget.
Try making fried rice so you can hide the meat and vege inside? Works for my LO, who also doesn’t eat meat and vege.. We chop very small and make fried rice or mash them with potato to make potato fritters