Simulations of the atmospheric pressure profiles, eclipse spectra, and JWST observations. Top-left panel: radiative-equilibrium thermal profile of TOI-396 b assuming a gas-giant atmosphere (5× solar metallicity) and a secondary atmosphere (80% H₂O plus 20% CO₂). Top-right panels: volume mixing ratio of TOI-396 b for the most relevant species shaping the infrared spectrum. Bottom panels: synthetic secondary eclipse spectra of the three TOI-396 planets (solid curves). The round markers with error bars show a realisation of JWST observation with NIRCam/F444W (and their expected uncertainties) when accumulating two, four, and eight observations for planets b, c, and d, respectively. The vertical dashed lines mark the spectral window covered by NIRCam/F444W.