Median mass-size relation of the TNG100 simulated galaxies and the observed datasets. Top: ETG galaxies from TNG100 (nETGs), SPIDER, and DynPop_nETGs (see inset for legend). Bottom: LTG galaxies from TNG100 and DynPop_LTGs, as in the legend. Error bars represent the 0.16, 0.84 percentiles of the data within different bins. We use log M_⋆/M_⊙ = 10.8, as a reasonable completeness limit based on the DynPop_nETGs and log M_⋆/M_⊙ = 10.3 for the LTGs samples.