Two fits to the metastable helium data of the mini-Neptune TOI-2134 b from Zhang et al. (2023a) assuming different atmospheric compositions. In panel a, we assume a pure hydrogen/helium atmosphere in the solar ratio. In panel b, we assume a 100 times solar metallicity atmosphere. The colors are the same as in Fig. 6, but here we do not use the model temperature self-consistency as a prior as we did in Fig. 6c. c) Observations from Zhang et al. (2023b) shifted back to the rest-frame helium triplet wavelength (black). Solid lines show the best-fit models from the blue contours in panels a and b. Dashed lines show models with self-consistent T₀-values from the orange contours in panels a and b. The self-consistent models produce lines that are too narrow, indicating that an additional line broadening mechanism may be at play.