If the manga is about the artist of the manga itself, (Say, if Artist A were to make a comic called "The Life of Artist A".) it would be an autobiographical manga.

The manga is about another artist, (Say, Artist A makes a comic about Artist B.) it would be a biographical manga.

If the manga is about a fictional manga artist, then it would depend on what genre the manga was. Drama, https://dream-manga.com/13729-super-rich.html comedy, etc.