The Add Field geoprocessing tool accepts in-memory geometry as valid input when used within ArcPy scripts and runs without returning any errors or warning messages regarding if, or where the output can be accessed.

Additional Information

Workaround

When running the above code within the Python window in ArcGIS Pro 2.2.2 with a map tab open, a new feature class is created within the default file geodatabase of the project. This feature class contains the previously constructed in-memory polygon geometry. Upon inspection of the attribute table of the feature class, the tabular schema consists of the newly-added field, along with other mandatory components of the file geodatabase polygon feature class tabular schema.

Steps to Reproduce