30011: Layer uses ArcGIS Desktop dimension <value>. Upgrade to ArcGIS Pro dimension for best results
Your map is drawing a dimension feature class that was created in ArcGIS Desktop 10.x. As a result, the dimension cannot be edited or modified in ArcGIS Pro.
The value lists the name of the dimension feature class in the message.
Solutions
Do one of the following:
Do nothing. Any feature class linked to it or in the same feature dataset will be read-only.
Upgrade the dimension feature class with the Upgrade Dataset geoprocessing tool.
Additional information
It is highly recommended to upgrade to ArcGIS Pro dimension feature classes as they support the full cartographic model. Dimension feature classes created in previous versions of ArcGIS Pro or ArcGIS Desktop may only be displayed and queried.