Baby food?

When did you all first introduce baby food to your LO? My baby is 3 months now and we use baby oatmeal cereal in his bottle to satisfy him more (he’s been wanting to eat over 10 ounces of just formula!).

I’m wondering when you all introduced baby foods. MIL is trying to get us to put baby food, like desert foods, in his bottle too, to satisfy him even longer. The jar of baby food we got is stage 1 from about 4 months plus, but I also know that doctors and mothers have differing opinions on when and what to feed their kid...