Relation between supermassive black hole mass and galaxy stellar mass, and its evolution with time. Top: M_BH–M_* relation at z = 2 in cosmosTNG. The gray line shows the linear relation and the 1 − σ scatter from Tanaka et al. (2025). The annotations and markers are as in Fig. 7, bottom panel. Bottom: Evolution of the offset from the local M_BH–M_* relation as described in Tanaka et al. (2025) based on Häring & Rix (2004), Bennert et al. (2011) for the local relation. The points with error bars show the high-redshift observations from Harikane et al. (2023) and Tanaka et al. (2025). The gray triangles show the observations from Sun et al. (2024). All observations are compared as-is (i.e., without corrections for the respective observational methodology used when compared to cosmosTNG). The green line shows the median relation in cosmosTNG for host galaxies with M_⋆ > 10¹¹ M_⊙. The shaded regions show the central 68%, 95%, and all percentiles respectively. The blue dashed line shows host galaxies with M_⋆ > 10^8.5 M_⊙. The observed galaxies with high black holes masses are rare but possible in cosmosTNG across z = 2 − 5.