I try the formula that IF({Date due}!=0,CREATED_TIME({Date due}),BLANK()), but the result is the created time of the row, not the date the {Date due} cell changes. What should I do?

Solved
How do you know when a cell changes
Best answer by ScottWorld
Create a field that is a “last modified time” field type, and choose to update it only when the Date Due field updates.
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