Unable to Set Column as ListItemMenu

I'm trying to set a column other than Title to be the list item menu. I've gone into Designer and updated the column with listItemMenu="TRUE" but this doesn't seem to be working. I've also tried List (capital L) and different variations on true, but nothing's working. Anyone have any tips on what could be going wrong?

This is Sharepoint Online, Modern view.

I'm going into Sharepoint Designer > Lists and Libraries > select the list > select the view (All Items) > locate the ViewFields tag > locate the FieldRef in question > add list menu coding. End result is:

<ViewFields><FieldRef Name="PO_x0020_Status" listItemMenu="TRUE"/>