How to create journal approval using DFF and use the same in approval spreadsheet

Summary:We are in the process of setting up journal approval using Descriptive Flexfields (DFF). We have created a DFF and assigned a value set to it. However, when creating the approval rule using the Journal Approval Spreadsheet, we have selected "USER" as the rule type, which makes the user name a mandatory field.
Could you please help us understand how this will work in conjunction with the DFF we have enabled?

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