The everviz application does not currently support marker clusters, however, all hope is not lost; the following image is the output of an everviz chart rendered in a JSFiddle:
The functionality is made to work by writing custom code which configures and enables the marker cluster module. You can view the options by following the reuse link provided here
https://app.everviz.com/create?uuid=5SW_5E4aE/?v=6
As seen in the JSFiddle, it is currently necessary to load this HTML before your chart:
<script src="https://code.highcharts.com/highcharts.js"></script>
<script src="https://code.highcharts.com/modules/marker-clusters.js"></script>
Where the first script reloads Highcharts, such that we can successfully load the marker clusters module.