Describe a time you automated a manual process using Excel.

This is the highest-value Excel story you can tell, because it converts your skill directly into money saved.

Structure it as:

• The manual process and its cost. Be specific: "four hours every Monday copying data from six exports and reformatting it" — that is roughly 200 hours a year, and stating it that way makes the impact obvious.
• Why it was error-prone, not just slow. Manual copy-paste introduces mistakes, and mistakes in a report that drives decisions are the real cost.
• What you built. Power Query is usually the right answer for anything involving importing and cleaning — it is repeatable, refreshable, and does not require anyone to learn VBA to maintain it. A macro is appropriate for interface automation. Say why you chose what you chose.
• The result. Time reduced, errors eliminated, and — importantly — whether it survived after you handed it over.

Note: Mention documenting it and training someone else. An automation only one person understands is a liability, and interviewers who have inherited an undocumented macro workbook feel this strongly.