Playing with version "ars_nouveau-1.16.4-1.11.2" and tried fighting the Ender Dragon and my two damage spells when collided didnt do any damage but did work on the endermen (and normal mobs).

2 Spells i used:

• Proj + harm + amp x 2 + fortune x3
• Proj + freeze + cold snap +amp x 3 + fortune x3

Didnt tried the Enchanted bow to see if that would of worked, thought i mention that

Freeze + cold snap won't work as the dragon cannot be given a potion effect, but harm should work in the next update.