Observational properties of the galaxy samples used throughout this work, selected according to the criteria in Sect. 2.4. Left: Stellar mass distribution of the JWST training set (black), the COSMOS2020 test sample (blue; 5000 sources randomly drawn from the full sample) and the mock CSST+Euclid catalog (dashed red; sharing the same sources as the blue sample but with parameters derived from reduced photometry). Middle: SFR distribution of the three samples. Right: The magnitude distribution of COSMOS2020 sample where we show the depth at 5σ for CSST.