It is a candidate chthonian planet, the exposed core of a gas giant that had much of its atmosphere stripped away.
[2] TOI-849 b is a high-density planet more massive than Neptune, about forty times the mass of Earth.
It orbits very close to its host star, with a period of less than one day, placing it within the Neptunian desert.
[1][3] Compared to other Neptune-sized exoplanets, this planet is unusually massive and dense.
This implies that any gaseous envelope of hydrogen and helium makes up at most 3.9+0.8−0.9 percent of the planet's mass.