Upper: Comparison of the forecasts from Euclid-like survey with analytical covariance, KiDS-Legacy with analytical and combined covariance and the KiDS-Legacy measurement of 95% bounds on the DM annihilation cross-section ⟨σ_annv⟩ for three final states of HIGH clumping scenario from combined covariance. The dot-dashed lines represent the expected cross-section $⟨{\sigma }_{\mathrm{ann}}v⟩=3\times {10}^{-26}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$. Lower: Forecast for three cases and KiDS-Legacy measurement of 95% upper and lower bounds on the DM decay rate Γ_dec for three final states. The model value of decay rate is taken as Γ_dec = 5 × 10⁻²⁸ s⁻¹.