The bug

The iron golem's reach is not as big as it used to be. In 1.20.1 and earlier, the golem could reach more than one block beyond the edge of its hitbox. Now, it can't even reach one block away from its hitbox.

How to reproduce

1. Spawn an iron golem that can't move:

   /summon iron_golem ~ ~ ~ {Attributes:[{Name:generic.movement_speed,Base:0}]}

2. Stand 2 blocks away from the iron golem:

   /execute at @e[type=iron_golem,limit=1,sort=nearest] run tp ~ ~ ~2

3. Attack the iron golem while in Survival mode
   → The iron golem doesn't attack you back (since you are out of reach)

Expected result

The iron golem should be able to attack you, as is observed in 1.20.1 and below (in these earlier versions, the iron golem's attack range is around 2.9 blocks).