Left: Evolution of the growth factor with the cosmic linear growth index γ. The bold black dashed line is the growth factor in Equation (7). Increasing γ reduces the slope of the growth factor, thus damping structure formation. Right: Power spectrum reduction model described in Section 5. We show the ratio of the modified power spectrum to the regular ΛCDM one for different values of the parameter β. The index is fixed to p = 1. Increased values of β reduce the structure formation at low redshift. These figures were produces using a Planck20 cosmology (TT,TE,EE+lowE+lensing+BAO).