f_exsitu as a function of stellar mass for model predications vs. ground truth. In the left panel the black solid curve is the median of the ground truth for the TNG100 galaxies; the blue and red solid curves represent those predicted by Model A (trained by TNG100) and Model C (trained by EAGLE); and the dashed curves are the ±1σ scatter. In the right panel the black curves are the ground truth for EAGLE galaxies; the blue and red represent those predicted by Model B (trained by EAGLE) and Model D (trained by TNG100).