Sometimes used as a term in linguistics.
Put it in quotes: "Indian Standard English" and you will see plenty of results.
https://www.google.com/?q=%22Indian+Standard+English%22
https://www.jbe-platform.com/content/journals/10.1075/eww.24...
It doesn't mean a written standard exists.
Maybe it's called Standard Indian English or just Indian English in other contexts; I'm only using a term I've seen used.