A geoprocessing service with the GPDataFile input type does not provide the option to upload a file in the Web AppBuilder for ArcGIS Geoprocessing widget in Portal for ArcGIS 10.7.1.
A fix for this issue is also available for ArcGIS Enterprise 10.7.1 as part of this patch: https://support.esri.com/en/Products/Enterprise/portal-for-arcgis/portal-for-arcgis/10-7-1#downloads?id=7749