Variance of the DEMNUni-Cov power spectrum. Top: Diagonal of the power spectrum covariance matrix in the 16ν cosmology, at z = 0 (blue) and z = 2 (purple). Solid lines show the variance estimated from the 50 DEMNUni-Cov realisations and the dashed lines display the Gaussian predictions. Bottom: Residuals between the estimated variance and the corresponding Gaussian prediction normalised by the error on the estimated covariance, given by Eq. (3). The grey areas represent the 1-σ and 3-σ levels of the residual.