A. Linear spectra Fig. presents the linear absorption spectra of a monomer coupled to the cavity by either varying cavity loss rate, Γ (Fig. ), or by varying the light-matter coupling strength, g c (Fig. ). The black curve in all panels represents the bare monomer molecular absorption spec-tra, with the broadening coming from couplings to collective bath-mode fluctuations. The red curves represent the spectra of a monomer coupled to a cavity mode.