Same as Fig. 9, but for the parameters of the ETHOS n = 0 model. Our forecast assumes logarithmic priors on the interaction strength a_dark and on the dark-radiation-to-photon temperature ratio ξ_idr. The model is equivalent to pure ΛCDM in the small a_dark and/or small ξ_idr limits. The grey shade excludes the region a_darkξ_idr⁴ > 0.05 where the non-linear emulator cannot be trusted (see Sect. 3.4). We also show current constraints inferred from Planck, BAO, and BOSS full-shape data by Rubira et al. (2023) – although these authors use different priors.