Upper: Forecast of 95% upper and lower bounds on the DM annihilation cross-section ⟨σ_annv⟩ for $b\overline{b},{\mu }^{-}{\mu }^{+}$, and τ⁻τ⁺ states from cross-correlation of ten energy bins from Fermi-LAT and ten redshift bins from Euclid-like survey. The expected value ⟨σ_annv⟩ = 3 × 10⁻²⁶ cm³ s⁻¹ is shown as dot-dashed lines for all cases. Lower: Forecast of 95% upper and lower bounds on the DM decay rate Γ_dec for $b\overline{b},{\mu }^{-}{\mu }^{+}$, and τ⁻τ⁺ states. The dot-dashed lines represent the expected value for the forecast with Γ_dec = 5 × 10⁻²⁸ s⁻¹.