Green’s Dictionary of Slang

(US) a phr. meaning that something is not worth bothering about.

1985		T.R. Houser Central Sl. 7: ain’t about nothin’ Forget it; it’s not worth the bother. ‘Fuck Jerry, man, he ain’t about nothin.’.
2017		S.M. Jones August Snow [ebook] ‘You was always cool with me,’ he said. ‘Ain’t about a thang, Snowman. Just remember: cash be kang’.