@Poutnik gave us the [Wikipedia link][1] which basically contains the answer:

>Lead tetroxide ("red lead"), a mixed oxide with formula $\ce{Pb3O4}$, may be thought of as lead(II) ortho-plumbate(IV), $\ce{[Pb^2+]2[PbO4]^4−}$. Lead sesquioxide, $\ce{Pb2O3}$, is also known, and has the structure lead(II) meta-plumbate(IV), $\ce{[Pb2+[PbO3]^2−}$.

Since $\ce{Pb3O4}$ contains $\ce{Pb(II)}$ and $\ce{Pb(IV)}$, it is lead(II,IV) oxide. Magnetite is actually $\ce{[Fe^{2+}][(Fe^{3+})2O4]}$, so it is iron(II,III) oxide.


  [1]: https://en.wikipedia.org/wiki/Plumbate