The "/damage" command does not inflict damage on ender dragons. However, it functions properly against all other entities, including non-living ones like items.

Steps to replicate

1. Enter the End dimension
2. Regenerate the ender dragon if it has been previously slain
3. If MC-146503 was not fixed, you would execute the command:

   /execute as @e[type=minecraft:ender_dragon] run damage @s 200 minecraft:arrow

   Alternatively, you can run:

   /damage @e[type=minecraft:ender_dragon,limit=1] 1 minecraft:arrow

Observed behavior: The ender dragon showed no signs of damage, as evidenced by the absence of sound, its failure to turn red, and the boss bar remaining unchanged.
Expected behavior: The ender dragon should have taken damage, resulting in it turning red, emitting the damage sound, and updating the boss bar.