In contrast to the short-time dynamics, the plateaued quantum-classical rate k, as demonstrated in Fig. (b), exhibits a dependency on the cavity frequency but lacks a peak structure. This stands in stark contrast to the findings of the fully quantum-mechanical study. To delve deeper into this disparity, we display in Fig. the rate modification k/k 0 inside the cavity as a function of the cavity frequency for three different light-matter coupling strengths η c , directly comparing the results from both the converged fully quantummechanical method and the mixed quantum-classical approach. Here, k 0 is the reaction rate outside the cavity, which is by definition identical for both approaches. In addition, we present fully quantum-mechanical results that involve only the lowest photonic state in the simulations. This serves to further demonstrate the role of photonic excitations in producing the peak structure in the cavity-induced rate modification.