Hi mum, when do you stop giving formula milk to your lo? Is it necessary to give milk until stage 4?

My mommy friends are rather extreme -- they usually breast milk for as long as they can (usually past 1.5 years) and when they stopped, they switched baby to cow/goat milk. But those who do put their baby through the formula stage in between only switched to cow's milk when their child is older, around 2-3 years of age,