Abstract: Understanding how massive quenched galaxies at z>=2, recently revealed in unexpectedly large numbers by JWST, form and evolve requires accurate models. I will first discuss challenges in semi-analytic models, where numerical artefacts in halo merger trees—such as mass swaps and sudden late-time halo formation—affect predictions at the high-mass end. I will then turn to the COLIBRE hydrodynamical simulations to examine the properties of these galaxies and the processes driving their rapid assembly and quenching. The results show reduced tension with observations once uncertainties are considered, while highlighting the role of environment and the contrasting outcomes of thermal-only versus thermal+jet AGN feedback.