Rest-frame radio luminosity at 8 GHz vs. the rest-frame optical luminosity at 4400 Å for PSO J191+86 (red star) compared with z = 4.5 − 5.5 radio-loud QSOs (gray points) discovered in the literature. Squares represent all the sources defined as blazars in the literature on the basis of their radio and/or X-ray properties. Yellow circles represent all the sources identified as peaked spectrum objects in the literature (Coppejans et al. 2017; Shao et al. 2020, 2022). PSO J191+86 is one of the most luminous RL QSOs at these redshifts, confirming the power of its radio emission.