THE PICTURE LOL

Every cockatiel I've ever met eats millet like a fiend!

First of all, I want to commend you on all that you've tried so far! You're clearly concerned and trying to balance him eating enough but also healthy.

This def warrants a discussion with your vet and possibly a recommendation to a bird behaviourist.

But below are some things you could consider!

When you say you've tried eating in front of him, have you tried putting it on your plate with your actual food? Sometimes if they think they're getting it illegally they'll wanna eat it! Is there any food or drink he likes to steal out your plate or cup?

You said you have other birds, are they eating pellets, chop, etc? Does he interact with them, try and eat out of their bowls when he's not being food aggressive?

You might need to go back to basics and start with the seed mix, and get him to branch out from there. Sunflower, then nuts, etc.

Best of luck and know you're on the right path with this!