Hi All. I'm using the Append tool in ArcGIS Pro, and in arcpy to try and both ADD new features to a feature service in ArcGIS Online (from a feature class), as well as UPDATE existing features if they match (Upsert).
From reading the documentation here I understand that the tool should look for features with identical attributes within the fields listed under the "Update Options" section. If a feature in the Input Dataset matches a feature in the Target Dataset based on those fields, then it will update all the fields listed in the Field Map (as well as the Geometry if that option is enabled at the bottom of the pane). If no matching feature is found, then those features in the Input Dataset should be Appended as new features.

However, the behavior I'm getting doesn't seem to match that. When I have no Update fields listed, the features in my Input Dataset are being appended as New features as expected. When I do have fields listed under the Update Options section, I am seeing matching features update but new features are not being added as I would expect.
Can someone clarify if there is a problem somewhere, or if I have my understanding wrong and the Append tool is either Add or Update, not both?
