  The planet GJ 367 b is a recently discovered high-density sub-Earth orbiting
an M dwarf star. Its composition was modelled to be predominantly iron with a
potential remainder of a hydrogen-helium envelope. Here we report an X-ray
detection of this planet's host star for the first time, using data from the
spectro-imaging X-ray telescope eROSITA onboard the Spectrum-Roentgen-Gamma
(SRG) mission. We characterise the magnetic activity of the host star from the
X-ray data and estimate its effects on a potential atmosphere of the planet. We
find that despite the very low activity level of the host star the expected
mass loss rates, both under core-powered and photoevaporative mass loss
regimes, are so high that a potential primordial or outgassed atmosphere would
evaporate very quickly. Since the activity level of the host star indicates
that the system is several Gigayears old, it is very unlikely that the planet
currently still hosts any atmosphere.
