M₁₄₅₀/z plane with all z >  6.5 quasars with published redshifts and luminosities at 1450 Å (red crosses), and a simulated Euclid wide survey quasar sample (black points), with random luminosities and redshifts drawn from the ground-based selection function (Fig. 8b). The blue dotted line indicates the redshift cut-off of this work. The green dashed contours indicate the apparent magnitudes considered in Sect. 5.3, in the context of ground-based follow-up spectroscopy and contamination. Discovery papers for the known quasars are: Mortlock et al. (2011), Venemans et al. (2013, 2015), Matsuoka et al. (2016, 2018a,b, 2019), Mazzucchelli et al. (2017), Tang et al. (2017), Koptelova et al. (2017), Reed et al. (2017), Wang et al. (2017, 2018, 2019), Bañados et al. (2018), Yang et al. (2019).