On sites that use the Leaflet map provider, the Enable Marker Cluster? checkbox may not appear in the explorer map settings.
Workaround. You can reveal the checkbox by temporarily switching the map provider to Google Maps. The setting is kept when you switch back.
- Change the map provider to Google Maps. Any placeholder text in the API key field is enough to show the Google-specific options.
- Tick Enable Marker Cluster? and save.
- Switch the map provider back to Leaflet.
If you would rather not do this yourself, contact support and they can turn it on for you.