I have subtasks enabled, and for one project I can create them. So I know what the icon looks like when working on building out a task and its subtasks.
But for no other project I've created in Jira is that icon appearing, and I've triple checked. Subtasks *are* enabled.
(I'm having a similar global configuration setting issue with logging time against a project: it's available for one project, but it's not showing for any of the others. So I'm hoping that the solution to this problem is something about the global configuration settings that can be made to populate to all the other projects.)