Why the electric field inside a solid sphere is non-zero according to gauss while we know that the electric field inside a conductor is zero?

We know that the electric field inside a conductor is zero, but in my book, according to Gauss’ law,
the electric field inside a solid sphere (it’s not mentioned if it’s a conductor or non-conductor) is
$$E = frac{Q}{4 pi varepsilon_0} frac{r}{R^3}$$