Dear ESRI Team.
In ArcGIS Desktop you can choose to check "Append" box when you want to add something coming from a new label in an existing annotation class. Why this DOES NOT exist in PRO?
It is loosing time to create first a new annotation class, then to mix it with the old one thanks to the "Append Annotation Feature Classes" tool, and then destroy the temporary annotation class. Working in PRO must be an improvement, not a regression.
Reference to existing option in Desktop: "If you are creating standard annotation and want to add the annotation to an existing standard annotation feature class, check the Append box. " in Converting labels to annotation—Help | Documentation .