According to Rambam, anyone learning full time without a parnassah creates a chilul HaShem and loses their part in Olam Ha-Ba!
That’s odd, because for a while the Ramba”m did just that, and was supported by his brother. I think maybe you are misunderstanding the Ramba”m.
R’ Moshe writes that it’s possible that the Ramba”m never held anything of the sort, but even if he did say something related to your misquote, the halachah does not follow him.