1. Download net5.0-refs.zip from the https://github.com/2sic/oqtane-razor-refs/releases/
  2. If Oqtane is installed from standard Oqtane.Framework.2.3.1.Install.zip release zip and hosted on IIS, unzip net5.0-refs.zip to your Oqtane.Server folder (root folder in IIS web site)
  3. When done - restart Oqtane and you're all set.