Stellar mass–size relation across redshift bins. All TNG50 subhalos are shown as light gray circles in the background, while selected compact subhalos are represented by dark gray circles. Observational CMGs from the different samples are indicated with white diamond markers. The solid black lines follow the mass–size relation from van der Wel et al. (2014), while the dashed gray lines highlight the selection region for the simulated sample (R_e < 2 kpc, log Σ_1.5 > 10.3 dex).