Installing the WFS FreeMarker Extension
Download the Features Templating community module from https://github.com/geoserver/geoserver/tree/2.26.1/src/community/wfs-freemarker.
Warning
Make sure to match the version of the extension to the version of the GeoServer instance!
Extract the contents of the archive into the
WEB-INF/lib
directory of the GeoServer installation.