Can callouts be created in ArcGIS Online Map Viewer?

No, creating callouts is not supported in ArcGIS Online Map Viewer. This functionality is currently only supported in ArcGIS Online Scene Viewer when working with 3D scenes. As workarounds, use label backgrounds in Map Viewer as a visual alternative or create callouts in ArcGIS Pro and publish the layer to ArcGIS Online.

Configure background labels in Map Viewer

1. In ArcGIS Online Map Viewer, open the web map. Refer to ArcGIS Online: View maps (Map Viewer) for instructions.
2. On the Settings (light) toolbar, click Labels .
3. In the Label features pane, turn on the Enable labels toggle button.

Note:
If no label class exists, add one before proceeding with the following steps.

4. Click Edit label style. In the Label style window, turn on the Background toggle button.
5. Under Background, configure the style as desired.
6. Close the Label style window and the Label features pane.

The map below shows the configured background labels in Map Viewer.

Create callouts in ArcGIS Pro

1. Open the ArcGIS Pro project.
2. Add callouts to the map. Refer to How To: Add leader lines to labels in ArcGIS Pro for instructions.
3. Publish or overwrite the web layer to ArcGIS Online. Refer to ArcGIS Pro: Share a web map using a chosen configuration or ArcGIS Pro: Overwrite a web feature layer for instructions.

The map below shows the callouts created in ArcGIS Pro and viewed in Map Viewer.