Comparison between the 68% and 95% confidence levels computed in this work with the void size function and different Euclid forecasts. Left: cosmological constraints on the Ω_de–w plane computed in this work (in blue) considering a wCDM scenario with fixed calibration parameters and in Hamaus et al. (2022; in magenta), modelling the void-galaxy cross-correlation function in redshift space, with a model-calibrated approach. Right: cosmological constraints on the Ω_m–σ₈ plane computed in this work considering a w₀w_aCDM scenario (in blue) with fixed calibration parameters and the marginalised IST Fisher forecasts computed in the optimistic setting with spectroscopic galaxy clustering (in purple) and weak lensing (in orange).