Does {{ content_for_index }} still works?

[Kamran2k19]

Does {{ content_for_index }} still work because I don’t get add section button in the theme editor? I have a template of index.liquid and it has {{ content_for_index }} in it so I can add sections dynamically. So do I have to use index.json for it now or might be I did it wrong and produce some error some error? If you try to reproduce it try doing it on a recently created store.