For finding the sum, ArcGIS pro really screwed it up.
In the original ArcGIS, you can easily find the sum by using the statistic of the raster.
ArcGIS pro now must ask you to use geoprocessing tools to get the sum. It becomes way less effective, especially if we consider the fact that ArcGIS pro has already helped us to estimate minimum, maximum, mean, and SD values but neglected the sum