After dying, Ender Dragon body part hitboxes do not move upwards with the main hitbox

Please provide a screenshot of this occurring with the F3 debug screen enabled.

Kinda hard to show a glitchy spazzy animation with a screenshot

That's 1.13.2, which is an outdated version that is no longer supported. This was Fixed in the 1.16 snapshots, see MC-164129.

No, it wasn't fixed. I will take yet another screenshot in vanilla 1.16.3 to show that this still occurs.

The bug you referenced was something obviously completely different to what this bug is reporting.

Affects 22w18a.

Confirmed in 1.19-rc2; might want to rewrite the report to be less arbitrary:
The body part hitboxes do not move with the ender dragon in its death animation, unlike the main hitbox.

While an ender dragon is dying, the main hitbox properly moves with the ender dragon into the sky.
This is not the case for the hitboxes for the body parts, which stay in place the moment its death animation begins, and vanish when the animation ends.

As of 1.19.4-pre1, when summoning a dying ender dragon with

/summon minecraft:ender_dragon ~ ~ ~ {DragonPhase:9}

while the portal area (0, 70ish, 0) in that dimension is not loaded, the dragon will rise up in place instead of attempting to fly to the portal. When this happens, its hitboxes will rapidly flicker in a line between its death point and the portal area, rather than simply flickering in place below the dying dragon. Manually killed dragons behave as before.

can confirm in 1.20.4

Relates to MC-272431, MC-271337, and MC-271336.