I noticed on this Youtube video from ESRI - https://www.youtube.com/watch?v=qkM5Bt9YGr8 that to group features you can use these handy up arrows, however in my Map Viewer I am unable to see any options for up arrows. They just are not there as all you can see are quantities ...
Are you using ArcGIS Online or enterprise? In ArcGIS Online we no longer have the up arrow but now use a checkbox to the left of the value where you can group, merge, separate, bulk move. You can check it out a blog on this here: https://www.esri.com/arcgis-blog/products/arcgis-online/mapping/bringing-order-to-complexity-value-g...
If you have a map that isnt showing those checkboxes in Online I can check it out for you if you can share it.