Set of one-zone chemical evolution models assuming the same IMF, stellar lifetimes, and stellar nucleosynthetic yields as in our cosmological hydrodynamical simulation. In the chemical evolution models, we assume SFE = 2 Gyr⁻¹, no galactic winds, and we vary the infall timescale from τ = 1 to 10 Gyr, with a step of 0.1 Gyr, to understand whether the inside-out growth of galaxies has an impact on the predicted He abundances. In panel a, the colour coding represents the infall timescale, whereas in panel b the colour coding represents the gas-phase metallicity.