ArcGIS experience builder "Stacked Bar Charts" requires stacking by category field like Dashboard's "Split by field".
Stacked charts currently only work based on having multiple value fields in 1 record, rather than a single value being assigned to a category in another field. I either have to post process my geometry data into summary information or use ArcGIS dashboard and embed into experience build to achieve this functionality.
There is no way in Experience builder to do the following stack chart/summary.
Say you have a road line dataset and wanted to stack length of road based on road type for different states. You want your X axis to be "State", your Y being sum of "Length" and your stacked categories to be "Road Type".