Fits of laboratory IR spectra of NH₄SH:H₂O ice mixtures at 135 K (sea green solid trace) and pure CH₃OH ice at 15 K (dash-dotted red or pink trace) to the 6.85 µm feature observed toward four protostars and two dense clouds (see Table 3). The total combined fits of both NH₄SH and CH₃OH are indicated with the dashed light blue trace. The best fitting mixture used in each fit is listed inside each panel. Note that many of the sharp spikes present in the JWST LYSO spectra are gas-phase lines in absorption (e.g., B1-c) or emission (e.g., L1527) rather than noise. Local continua used to extract the feature from the observational spectra can be found in Figure E.2.