Plugin Value Setter doesn't work correctly for Excel workflow. Values are not getting updated in Sharepoint column.
Value setter node work only with form fields and form xml of the form.
It is not supported to work on Sharepoint Library columns.
In order to update Sharepoint library columns,you can use set column plugin with "uselinkeddocument" property set to "yes". With this settings you can update the value of Sharepoint library column.
Set column plugin documentation:-
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