Time evolution of the gwIMF (right panels) and the stellar mass-to-light ratio in the K-band (left panels) assuming a constant SFR of ψ = 10³ M_⊙ yr⁻¹ (top panels), 1 M_⊙ yr⁻¹ (middle panels), and 10⁻³ M_⊙ yr⁻¹ (bottom panels) over a timescale of 14 Gyr in the invariant canonical gwIMF (dashed black lines in the left and right panels; Kroupa 2001) and IGIMF-2021 (solid black line in the left panels and coloured lines in the right panels) framework. The chemical evolution model adopts g_conv = 0.25. The mass-to-light evolution curves adopting the invariant canonical IMF are not identical because they represent the evolution of galaxies with different metal enrichment histories.