The correct option is Set the trigger to When value changes for "Due Date" then check that the issue has a parent and branch to the parent and if the parent "Due Date" is before the trigger issue due date then edit the parent "Due Date"

This option works because the rule runs only when a due date changes so it reacts to sub task updates and the condition that the issue has a parent ensures it does not run for standalone issues. Branching to the parent lets the rule evaluate and update the parent issue directly and the compare that updates the parent only when the parent due date is before the sub task due date ensures the parent becomes the maximum of its sub tasks without lowering the parent when a sub task is earlier.

Configure a When value changes for "Due Date" trigger then require that a parent exists and run a branch over sub tasks and if any sub task has a later due date than the trigger issue edit the issue field "Due Date" is incorrect because it branches over sub tasks and then edits the trigger issue. That approach would modify the sub task rather than updating the parent and it does not directly set the parent to the latest sub task date.

Use an Issue updated trigger then verify that a parent exists and branch to the parent and if the parent "Due Date" is after the trigger issue edit the parent "Due Date" is incorrect because the comparison is reversed and would try to edit the parent when the parent date is already later. The trigger is also broader than necessary which can make the rule run for unrelated updates.

Trigger on When value changes for "Due Date" then confirm a parent exists and if the trigger issue due date is after the parent "Due Date" then edit the trigger issue "Due Date" is incorrect because it edits the sub task instead of the parent. The logic should update the parent when a sub task is later so that the parent reflects the maximum due date among its children.

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