Within ArcGIS Pro 2.4.1 if a user formats multiple categories symbols, the Layers button and Structure button are missing from the Properties section of the Symbology pane.
Formatting only one class's symbol then all three buttons (Symbol, Layers, and Structure) are visible within the Properties section of the Symbology pane.
Duplicate of BUG-000108431: This is as designed. See https://pro.arcgis.com/en/pro-app/help/mapping/layer-properties/symbols.htm#ESRI_SECTION1_9F5479183BBF44FD9647FEE80072C137
We may enhance this user experience in the future.