User wants to create a filter to show for example issues that are open, with X version and all of those issues subtasks.
Today, you can search for issues subtasks by specifying the issues "parent".

ex of JQL code:

status = Open AND affectedVersion = <version> AND parent = <issue key OR Id>

So, the user wants to show all issues based on certain criteria and whatever subtasks these issues have, not specific issues subtasks (without having to specify the issues "parent").

A known current workaround is documented at HowTo: Filter to show sub-tasks of a filtered list of parent tasks .