The mass-temperature relation for galaxy groups and clusters in simulations, with mass defined inside R₅₀₀ as a function of X-ray temperature. Blue background points represent individual mass-weighted temperatures for each simulated group in MAGNETICUM. Black squares correspond to stacked bins from eRASS1 observations. Open diamonds represent background modeling instead of background subtraction. The red line shows the scaling relation from (Lovisari et al. 2015), the green dashed line represents the self-similar model, and other lines depict results from FLAMINGO (Braspenning et al. 2024) and EAGLE (Barnes et al. 2017).