The paper presents the first JWST NIRISS/SOSS transmission spectrum of LTT 9779 b, a hot-Neptune planet with a significant H/He-dominated atmosphere. The 0.6 – 2.85 μm transmission spectrum shows muted spectral features, rejecting a perfectly flat line at >5σ. The authors explore water and methane-dominated atmosphere scenarios and find that the atmosphere's metallicity is constrained to be between 20–850× solar. Retrieval analyses reveal a continuum of potential combinations of metallicity and cloudiness, with a preference for solutions with clouds at mbar pressures, regardless of the dominant atmosphere component (water or methane). Cloud-free atmospheres with metallicities >500× solar cannot be ruled out. The presence of silicate clouds at mbar pressures is confirmed through comparisons with self-consistent atmosphere temperature profiles and cloud condensation curves. The advection of these clouds onto the day-side could explain the high day-side albedo previously inferred for this planet, potentially forming a feedback loop that aids the survival of LTT 9779 b's atmosphere in the hot-Neptune desert.The paper presents the first JWST NIRISS/SOSS transmission spectrum of LTT 9779 b, a hot-Neptune planet with a significant H/He-dominated atmosphere. The 0.6 – 2.85 μm transmission spectrum shows muted spectral features, rejecting a perfectly flat line at >5σ. The authors explore water and methane-dominated atmosphere scenarios and find that the atmosphere's metallicity is constrained to be between 20–850× solar. Retrieval analyses reveal a continuum of potential combinations of metallicity and cloudiness, with a preference for solutions with clouds at mbar pressures, regardless of the dominant atmosphere component (water or methane). Cloud-free atmospheres with metallicities >500× solar cannot be ruled out. The presence of silicate clouds at mbar pressures is confirmed through comparisons with self-consistent atmosphere temperature profiles and cloud condensation curves. The advection of these clouds onto the day-side could explain the high day-side albedo previously inferred for this planet, potentially forming a feedback loop that aids the survival of LTT 9779 b's atmosphere in the hot-Neptune desert.