ArcGIS Insights versions 1.0 to 2.3 have been retired. The archived help for Insights in ArcGIS Enterprise 1.2.1 and 2.3 is available for download in PDF format for all languages that were supported at the time of the software release.
Insights 1.2.1 is the latest version that supports ArcGIS Enterprise 10.5.
If you are using Insights 2.3 with ArcGIS Enterprise 10.5.1 or 10.6, you can upgrade to Insights 3.1.
Download the 1.2.1 documentation.
Download the 2.3 documentation.
For more information, see Compatibility with ArcGIS Enterprise.