The Standard Model (SM) of Particle Physics is the pinnacle of the understanding of neutrino physics Deppisch (2019); Oberauer et al. (2020). It comes with a plethora of parameters, the masses and the flavour mixings, that are seemingly not fixed by any known fundamental principle. In the SM, the neutrino spectrum is simple: all neutrinos are massless. Neutrino oscillationsNeutrino, oscillations, where neutrinos seemingly change flavour in flight, cannot be accommodated in the SM due to the mass of the neutrinos. Neutrino oscillationsNeutrino, oscillations thus imply massive neutrino eigenstates, and the SM must be extended. Moreover, neutrino oscillationNeutrino, oscillations experimental data suggest that the neutrino spectrum is not hierarchical, with three massive light neutrinos and a mixing matrix exhibiting near-maximal mixing Deppisch (2019); Oberauer et al. (2020).