The Ender Dragon hitbox is broken in 19w08b. This is extremely noticeable when trying to swing at it below from the fountain, or while trying to hit in in creative while it's circling the arena. The only two places where the hitbox is not broken are the head/upper neck and near the middle of the tail. Everywhere else the dragon is intangible from melee attacks, unless the player is jumping inside the dragon's visual hitbox (the green one shown with F3+B), in which case they can do damage to the middle section of the body. This can be easily seen by using a weapon with sharpness/smite/bane of arthropods, because you can see the particles when you hit an bugged intangible section of the dragon hitbox.