Colour-magnitude diagram for M dwarfs in the TESS SCVZ (cyan) with the two samples defined in Sect. 3.4 highlighted in green (count rate ≥ 1 cts s⁻¹) and red (count rate ratio between eRASS2 and eRASS3 ≥ 2 cts s⁻¹). The overlap between the two samples are marked in orange. Overplotted is the main sequence isochrone (black) from the table ‘A Modern Mean Dwarf Stellar Color and Effective Temperature Sequence’ by E. Mamajek (https://www.pas.rochester.edu/~emamajek/EEM_dwarf_UBVIJHK_colors_Teff.txt).