What is something scientifically moot that is still in practice?

I feel like i may be misinterpreting your meaning or you may misused “moot”

But i’ll go with people believing that orange juice helps with curing the cold/flu.

Vit C can be preventive, but also the amount needed is very low and you can’t increase it by drinking more. In reality you only need to eat an orange like once a month to get the required amount for your body and after that, any extra is just flushed out with urine.