This is now live — numeric and monetary custom fields on Opportunities can be used directly as metrics (Sum, Min, Max, Average) in dashboards and reports. If you're tracking revenue won in a custom field, you can build a widget summing it directly, without relying on invoice data.

Details: https://help.gohighlevel.com/support/solutions/articles/155000008495-using-custom-fields-as-metrics-in-dashboards-and-custom-reports