Neutron star mass–radius diagram. The solid lines represent the mass–radius relationship of typical EoSs. The grey shaded regions are forbidden by general relativity, finite pressure (P < inf), and causality. The yellow shaded region is forbidden by the rotation of the fastest spinning pulsar J1748−2446ad (Hessels et al. 2006). The red shaded region shows the mass of J0740+6620 (Cromartie et al. 2020; Fonseca et al. 2021) and the orange region the mass of J1614-2230 (Demorest et al. 2010), the two heaviest known NSs. Valid EoSs need to cross those regions. The green line and green shaded region would be forbidden if the quasi-period of FRB 20201020A were produced by the rotation of a NS at 2435 Hz, and the region to the right of the dashed green line would be forbidden if the rotation was at 1205 Hz.