Not sure if this will help but we have a "scraps bowl" for our little one which seemed to really help with this, just an empty bowl they can put the food in they don't want yet or just want to throw!
We still use a high chair, and he's always been a thrower so we just put a few bits on his tray at a time!
My daughter is doing the same, everything I put in front of her she just throws. No advice but I feel your pain 😩 xx
My little boy does this when there’s too much in front of him. I literally have to put tiny portions down wait for him to finish then give him more. Sometimes I’ve got to let him out his high chair so he can walk round eating