Anticorrelations between the Fe II strength, parametrized by R_{Fe II}, the [O III] EW, and HβFWHM. Top panel: the anticorrelation between R_{Fe II} and EW_{[O III]} (EV1 relation). PJ308-21 (blue diamond) shows a value in agreement with both low-redshift (Shen et al. 2011), 1.5 < z < 3.5 (Shen 2016) and z > 6 quasars (Yang et al. 2023). Bottom panel: anticorrelation between R_{Fe II} and FWHM(Hβ) (2D EV1). Also in this case, the PJ308-21 value appears consistent with the findings of other studies.