Ahem.

M Class planets have large amounts of water and a nitrogen/oxygen atmosphere, and a temperate climate.  In other words, humans can live there with minimal terraforming. Just because the planet is not instantly lethal to all forms of life does not make it M Class.

The planets scientists are finding tend to be in the I, J , S or T gas giant classes. And now that they think they have found rocky planets, until we know what their atmospheres are like we can’t classify them.

Thank you for your attention in this matter.