(Left) Evolutionary track of TOI 5398 up to an age of 5 Gyr in the effective temperature–bolometric luminosity plane. A black cross marks the current location of the star on the track. (Right) Time evolution of X-ray (5–100 Å), EUV (100–920 Å), and total XUV luminosity of TOI 5398, according to Penz et al. (2008) and the X-ray/EUV scaling by Sanz-Forcada et al. (2022). The grey area is the observed 1σ spread around the median (dark grey line) of the X-ray luminosity distributions for dG stars in the Hyades and Pleiades open clusters. Uncertainties on the age and X-ray luminosity of TOI 5398 are also indicated.