Item drops from iron golems and cats aren't affected by looting enchantment. Here's the list of item drop without looting enchantment

• Iron Golem drops 3-5 iron ingot and 0-2 poppies
• Cat drops 0-2 string

Those list doesn't increase item dropping when using looting enchantment

Steps to Reproduce:

1. Make sure to enchant your sword with Looting 3, using /enchant @s looting 3
2. Summon Iron golem and cats
3. Kill it using the sword enchanted with looting and observe the loot that it drops upon death

Observed Results:

• Kill Cat doesn't increase string drop, only drops max 2 strings
• Kill Iron Golem doesn't increase Iron Ingot and Poppy

Expected Results:

Both cat and iron golem drops would be affected by the looting enchantment.