As far as I am aware, it is not possible to generate a drop-down list using a formula rather than data validation, however, the following approach might be utilized to meet your needs.
- A page layout like this:
Data validation formula as following:
- And also alert option will be disabled ( to be able to add custom data):
- When you write "List" in the cell "A2" you will get the Column C in the drop down list and if you do not write anything in cell "A2" you will get D column in the drop down list.