^This^

I put the grate back in my cage when I caught my budgie foraging fallen millet around his poop.

u/OP you can also tuck some millet pieces in his toys to find and forage. To discourage him from actually throwing the food, you can try using an enclosed feeder like a seed corral or buy him a shallow cat bowl like https://www.amazon.com/Petrageous-Designs-City-Pets-6-25/dp/B000HVIQGC/ so he can move move around without wanting to toss it. Cat bowls are also great for serving chop.