This issue functions directly as an inverse of MC-272899.
Arrows shot from bows or crossbows enchanted with knockback will cause the attacked entity to be knocked back depending on the enchantment level, despite the punch enchantment existing for specifically bows and crossbows, with knockback being used for melee weapons.

Steps to Reproduce:

1. Get a bow or crossbow enchanted with knockback

   /give @p bow[minecraft:enchantments={knockback:2}]
   

2. Shoot an entity that can take knockback
3. (optional) For comparison, shoot an entity with a normal bow

Observed Behavior:

The entity is knocked backwards from the arrow.

Expected Result:

Because the entity is attacked via a fired projectile and not being attacked by the bow item itself with a melee attack, the entity would not be knocked back. Punch would be required to get the desired effect.

Screenshots/Videos:

Here, the bow is enchanted with knockback II.
EntityKnockbackBow.mp4

Notes:

Related to MC-272899 MC-196747