Redshift evolution of the median Sérsic index (n, top), median ellipticity (ϵ = 1 − b/a, middle), and quiescent fraction (bottom) for Brightest Group Galaxies (BGGs, red circles) and a stellar-mass-matched field sample (blue squares), based on the combined NUV–r–J plus sSFR classification (Sect. 2.4). Error bars represent the 16th–84th percentile range (n and ϵ) or binomial uncertainties (quiescent fraction).