I’ve heard you shouldn’t look at their diet meal by meal but rather by week - it’s ok to not eat any veggies one meal if they’re eating some the next meal or day etc. Also, have you looked at proper portion size for a toddler? I was quite shocked that eg 1-2 florets of broccoli counts as a portion, so they sometimes only need a tiny amount of it to be enough.

My 3yo son almost never eats everything he’s served but I think that’s because he’s in tune with what his body wants to eat. We’ve never forced him to eat and I think it’s been positive overall because he enjoys exploring different tastes at meal times without pressure. Sometimes he’s gone through weeks long phases of eating barely anything or only wanting bread and cucumber, but nowadays he’s really adventurous.

Personally I grew up in a house where I was expected to eat everything on my plate, which was an arbitrary amount decided by my parents. Often it meant being forced to eat when I was already full, which I don’t think has given me the best relationship with food. I think it’s more important long-term to develop a good relationship with food than to think about what’s going into their mouth right now.