I'm using arcgis 10.7.1 so perhaps some works now?
In arcgis online or in portal ur able to pick a map image layer and change its symbology, remove or reorder layers. and then save it, what u can't do is save as, it would be great if that could be implemented in portal and agol to save a new version of your map image layer.
what u can do today is add your service again to portal or ago and then change your map image layer and save it, but thats many steps and a lot of hassle.
also it would be great if it would be possible to change symbology in arcgis pro since its doable in portal and agol, i can't believe its not possible yet in arcgis pro?
if u can't do it in pro then the ability to use portal or agol as a central role in your arcgis pro flow will be somewhat lost.
