Hi @Samuelraj As it's a team managed project, you can only apply Restriction/Condition on Close transition, that only certain people close the parent task and create an automation rule when all Sub-task are closed to automatically move parent to Close status.
OR
You can do one thing, creates an automation rule to move Parent task back to the previous status or some other status if all the sub-tasks are not in Closed status. Similar to below screenshot.
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