^^ The Enderman is never supposed to be hit by a projectile of any type, excluding Positive potions and Large Fireballs(I think?). The reason being it teleports away just a few ticks before the projectile would hit.
Please Note: I first figured out this issue on Bedrock Edition iOS. I do not know if it applies to LCE or Java.
I re-tested it in Vanilla 1.16.2 and the same thing did happen. My bad! Also just for proof I re-uploaded the screenshots in 1.16.2 Vanilla.