Top: G-magnitude distributions (left) and T_eff distributions (right) of the total XGBoost sample cross-matched with AspGap (in grey) and the subsample for which differences in metallicity are smaller than 0.1 dex (in red); see Sect. 2. Middle left: comparison between the XGBoost and the AspGap metallicities, colour-coded by T_eff. Middle right: zoomed-in view of the high-metallicity regime. Bottom: same as the middle plots but colour-coded by the G magnitude. Black contour lines represent 33, 66, 90, and 99% of the sample. The solid red line represents the 1:1 relation, whereas the dashed ones are shifted by ±0.1 dex.