The `OFFSET` function adjusts cell references dynamically, helping create drop-down lists that update as new data is added.

Learn to create efficient, interconnected Excel drop-down lists using range functions and data validation techniques. Multi-level drop-down ...

If you’re not already sure how to add a drop-down list in Google Sheets, start with this quick guide. Once you have one in your spreadsheet, we can move into App Script to modify the code.