We theoretically investigate electron–surface optical phonon (SOP) interactions mediated by long-range Fröhlich coupling in monolayer platinum diselenide (PtSe₂) and platinum disulfide (PtS₂) supported on SiO₂ and hexagonal boron nitride (hBN) substrates. Using an effective Hamiltonian approach near the K₊ and K₋ valleys of the hexagonal Brillouin zone, we analyze electronic energy renormalization, polaronic oscillator strength, and SOP-induced scattering rates. Our findings reveal a strong dependence of the interaction strength on the dielectric properties of the substrate, with higher optical phonon energies and larger static permittivities leading to reduced carrier scattering. Moreover, increasing the van der Waals interfacial spacing significantly suppresses scattering due to the exponential decay of the electric field, thereby enhancing carrier mobility and optical performance. These insights underscore the importance of substrate selection and interface engineering as key strategies for tailoring electron–phonon interactions in 2D optoelectronic devices.