As of 1.21.8, mobs are not able to use crossbows anymore. They try to fire the arrow, but no arrow ever appears.

This appears to be caused by onFireArrow in RangedWeaponItemMixin returning null instead of original::call whenever it's used by non-player entities (see RangedWeaponItemMixin#L45).

To reproduce:

1. Spawn a pillager.
2. Switch to survival mode.