<p>This study investigates the impact of cross-diffusive effects on the onset of double-diffusive convection in a horizontal fluid layer, considering the influence of temperature-dependent viscosity and gravity fluctuations. The authors proposed six different categories of gravity fluctuation. The linear analysis is performed using the standard mode technique. A single-term Galerkin approximation, with the Mathematica tool, is used to derive the critical Rayleigh number and neutral stability curves. The findings indicate that the extent of the convective cell enlarged with decreasing gravity variation but decreased with increasing gravity fluctuation as the gravity and viscosity parameters were increased. As the temperature of a liquid increases, its viscosity usually decreases. This connection can significantly impact the fluid's motion in a double-diffusive system. The stability of double-diffusive convection may be influenced by the viscosity, which is temperature-dependent. A lower viscosity may make instabilities worse, whereas a greater viscosity may make them better. Also, it is clear that case (iv) is less stable than case (iii). These results help us gain a deeper understanding of convective events and pave the way for further research into how these factors interact in various fluid systems. Ultimately, this study offers up new paths for discovery, challenging old paradigms and allowing scientists to explore further into the intriguing domain of fluid dynamics.</p>