I Don't found kt_chart_widget_8_month_chart Documentation.
Please find the initialization script of this widget in
src/js/widgets/charts/widget-8.js. This widget uses ApexCharts plugin to display the charts.
Then recompile your assets folder with Gulp or Webpack.
Please note that the build tools are required only in the development environment just to compile the assets when the source folder files are modified. In the hosting/server deployment you will only need the compile assets, no need to install the build tools dependencies there.