The theory k VSC (Eq. 16) explains the collective effect, where both the collective solvent-solute coupling Λ as well as the collective light-matter coupling Ω R show up in the rate constant expression. When there are no disorders for light-matter couplings (χ = 1) and all Q j -R 0 couplings C j are identical, the dark vibrational modes are completely decoupled from R 0 , thus not influence the reaction rate constant anymore. We found that a distribution of the C j couplings and the angle (φ j ) between the molecular dipole and the cavity field will determine the impact of the dark states on the rate, and the dark vibrational modes will not dominate the spectral density J eff (ω) with a moderate distribution of C j and when the light-matter interaction angles {φ j } ∈ [0, π/4] with an isotropic distribution. Beyond that, the magnitude of the dark modes' spectral density dominates over the polariton peaks (see Supplementary Note 5) and the rate constant is reduced back to the outside cavity case (i.e., VSC effect diminished).