Different diagnostics of the evolution of specific dust masses in QGs, as simulated with the SIMBA full-volume simulation run. Upper panel: modelled M_dust/M_⋆ as a function of Z_gas in SIMBA. Circles represent the modelled QGs within the restricted range of dust-to-gas mass ratios (1/20 < δ_DGR < 1/100). Grey contours show the distribution of all QGs selected in the simulations with the criteria described in Sect. 6.1. The points are colour-coded by δ_DTM, with circle sizes scaling to f_gas. The inset sketch qualitatively describes the behaviour of M_dust/M_⋆: up to a certain Z_gas it mostly resembles the change in the molecular gas fraction, while at 12 + log(O/H)≳8.9 it reflects the level of dust growth through the gradual increase in δ_DTM. Lower panel: evolution of M_dust/M_⋆ with f_gas for the same simulated sources plotted in the upper panel. The dashed blue and orange lines show median trends for two regimes of Z_gas, as indicated in the legend. The effect of an increased dust growth in QGs is most pronounced in sources with heavily exhausted gas reservoirs, as indicated by the lower molecular gas fractions (f_gas < 1 − 5%). To highlight this effect through the rise in δ_DTM, we sketch the shaded area between the two tracks and colour-code it to roughly match the colour bar convention from the upper panel.