I need all subtasks to show up as collapsable under their parent issues in my Kanban Backlog

Hi @Sidra Hussain and welcome to the Community!

The post you refer to has a screenshot from Jira server. You seem to be on cloud and Jira has evolved a lot, having multiple types of projects (Jira Software, Jira Work Management, Jira Service Management, Jira Product Discovery) and flavours (company managed vs team managed).

In Jira Software's backlog view, I am seeing the exact behaviour you describe:

However, when you say you have tried swimlanes you seem to be referring to the active sprint or board view instead of the backlog. Those are different things and they do behave differently (as they serve different goals).

If you want more information, please share more details (like e.g. a screenshot) of your setup, so we can assess better where you are in the application.

Hope this helps!