Nuclear disc mass build-up. In this plot we present the nuclear disc mass normalised by the galaxy mass for different bar ages. To measure the nuclear disc mass, we integrated the isolated SFH (blue dashed curves in Figs. B.1 and B.2), following the same approach in de Sá-Freitas et al. (2023a, b). Additionally, we color-coded each point according to its Σ_SFR, which increases towards blue. It is clear that young nuclear discs are less massive with a higher star formation rate. As the bars age, the nuclear discs gradually present less star formation, while building up their mass. Lastly, we find a correlation coefficient of 0.85±2×10⁻³, with p-value = 2×10⁻⁴±7×10⁻⁵.