Galaxy stellar mass function at redshift z = 0 from simulations and GAMA observations (Driver et al. 2022). For comparison, all properties have been converted to a h₇₀ cosmology, with masses from simulations scaled as $h_{70}^{-1}$ and masses from observational data scaled as $h_{70}^{-2}$. The vertical dashed lines indicate the stellar mass cuts applied to the two FLAMINGO simulations, based on their respective resolutions. The overall agreement between simulations and observations supports our approach for estimating the total stellar masses of mock galaxy groups, while the resolution limits of the FLAMINGO simulations highlight the need for careful treatment, as is detailed in Sect. 3.4.