Boiling water does ruin formula if you add the formula to the boiling hot water before allowing the boiled water to cool down.
You should boil water before making formula but always allow the water to cool down to around 158 F before you add the formula.
The boiling water when mixed with the formula damages the nutrients in the formula that the baby needs to thrive.
The reason why you should wait 30 minutes before making formula is to allow the water to cool after boiling to a cool enough temperature that is hot enough to kill off bacteria in the formula powder but not hot enough that it damages the nutrients in the formula or poses a risk of scalding to the baby.
The water should be cooled to at least 158 F after boiling of the water to make the formula.
Make sure you also mix the proper amount of formula with the water and don't add too little or too much.
If you don't add enough formula powder to the water then the baby won't get the proper nutrients to thrive and gain weight.
If you add too much formula to the bottle the baby could have digestive issues and become dehydrated as a result of the baby formula being overly concentrated.