The origin of the cosmic neutrino signal measured by IceCube is still unknown. A general correlation between the sources of high-energy $\gamma$-ray sources with IceCube neutrinos is expected since hadronic interactions are the crucial precursors of both messengers at such high energies. Blazars dominate the extragalactic $\gamma$-ray sky. However, neutrinos originating from inside the blazar jets cannot account for more than $\sim30\%$ of the diffuse flux. We study ultrahigh-energy cosmic-ray contribution to the diffuse flux through photopion interactions on cosmic background photons. The extragalactic background light, consisting of IR/UV/optical photons require a proton energy threshold of $E_{\rm th}^{p,\pi} \approx 10^{17}$ eV for pion production. The latter can yield PeV neutrinos. We analyze the total contribution from resolved and unresolved blazars by using a luminosity-dependent density evolution of blazars. The latest Fermi-LAT 4LAC catalog sheds light on the redshift distribution of the diffuse neutrino flux for resolved $\gamma$-ray blazars.