Kernel density estimation of [X/Fe] (with X = C, N, O, Mg, Al, Si, or Ce) with metallicity (a–g), and [Al/Fe] as a function of [Mg,N/Fe] ratios (i,h) for the APOGEE DR16 stars (grey contours) surviving the quality cuts discussed in Sect. 2 and corresponding to the chemical domain of the halo, and low-metallicity end of the bulge and disc, corrected by the offsets between pipelines (see Fig. D.2). ω Centauri stars (cyan contours) from Mészáros et al. (2020) are also plotted for comparison. The black and lime star symbols refer to Al-rich stars in the bulge sample and outside the bulge region, respectively. Our sample is compared to GCs (crimson violin representation, indicating with horizontal lines the median and limits of the distribution; left to right: M 53, NGC 6397, NGC 5466, M 55, M 22, M 79, NGC 6752, M 13, M 2, NGC 6544, M 3, M 54, M 10, NGC 6522, NGC 3201, NGC 6229, Pal 5, NGC 288, M 5, M 12, NGC 1851, NGC 362, M 4, NGC 2808, Pal 6, and M 107) from Mészáros et al. (2020), and a sample of selected NRS (pink hexagons) from Schiavon et al. (2017) with available APOGEE DR16 abundance ratios. The plotted error bars (green symbols) show the typical uncertainties associated with our sample.