Arcade FeatureSet, how to get the FeatureSet for current selected features?

[ChenLi]

I like to configure a popup to display sum of selected features. 

sum($layer,'field_number') will sum all features, selection was disregarded.

[DavinWalker2]

Hi Chen,

Try sum($feature,'field_number')

[ChenLi]

Sorry, sum($feature,'field_number') displayed nothing for my ArcGIS Pro 2.7