Summary:
Llama spit has the capability to inflict damage upon ender dragons in flight atop the end portal, a feat not achievable by other projectiles like arrows and tridents. This is related to MC-85897. (It seems that projectiles are generally only able to damage ender dragons when they have a player as an owner.)

Steps to reproduce:

1. Go into the end.
2. Respawn the ender dragon if it has already been defeated.
3. Put the following command into an activated repeating command block:

   execute as @e[type=minecraft:llama_spit] run data modify entity @s Owner set from entity @p UUID

4. Wait for it to soar above the end portal.

5. /execute at @e[type=minecraft:ender_dragon] run summon llama_spit ~ ~10 ~ {Motion:[0.0,-1.0,0.0]}

Observed results:
The llama spit damages the ender dragon despite it being above the end portal.

Expected results:
The llama spit should not be able to damage the ender dragon, since it is above the end portal.