Activity-rotation relation in terms of L_x/L_bol vs. P_rot and based on the SpT-color code. As in Figs. 14 and 15, we present the deepest X-ray luminosity, including the upper limits (upside-down open tria-gles) as a function of rotation periods extracted from TESS light curves or calculated from υ • sin i measurements when the rotational modulation do not provide a clear value (left-oriented arrows). The UCD sample of this work (open circles) is compared with the M dwarfs studied in Magaudda et al. (2020, 2022), see Sect. 5.