How to tell if input is already registered

[MikulasLebowski]

Is there a way to check if input is already registered?

When setting initial values in useEffect, the setValue cannot be used in a straight-forward way because apparently the inputs are not registered at that point. It works when I put setTimeout(..., 1) into the useEffect, but that is of course horrible way to do anything in react.
Is there a way to check if inputs were already registered with the form hook?

It would be amazing if you'd added something like "onInputsRegistered" callback option.

I cannot use "defaultValues".