The evolution of the Quasar Luminosity Function (QLF) across cosmic time presents several puzzles. While the number density of luminous quasars peaks at $z \sim 2-3$ ("Cosmic Noon") and declines sharply towards higher redshifts ($z > 6$), recent observations reveal a surprisingly high density of supermassive black holes (SMBHs) already in place at $z \sim 7$. Reconciling the rapid assembly of these $10^9 M_\odot$ monsters with the observed faint-end slope and the relatively short time available for accretion is challenging for standard $\Lambda$CDM models, often requiring continuous super-Eddington accretion or massive seed scenarios. Additionally, the specific shape of the QLF evolution—pure luminosity vs. pure density evolution—remains debated.