Stellar mass size relation for the full sample of Euclid galaxies. From left to right, panels depict the distribution of retired, quenched, ageing, and the three combined classes across the parameter space. Solid and dashed lines denote the 16th, 50th, and 84th running percentiles computed using the Posterior- and KDE-based classifiers, respectively, adopting the criteria that maximises the F-score. The dotted dashed lines denotes the best-fit of Eq. (15) to the percentiles. Top and bottom coloured background maps illustrate the median value per bin of the inferred median stellar metallicity and Sérsic index, respectively, where only bins with more than ten galaxies have been considered.