In ArcMap, I constantly use the Label Manger to tweak 40+ Maplex label classes to meet a particular demand, which is fast and easy as I can just pick any label class from the manger, make a change, hit apply, make another change, hit apply, see what cartographic effect my changes had....
In Pro, as far as I can tell (unless this critical label management tool is just buried somewhere, unfound by me), the same process is to, in a Layout, highlight each labeled layer in the map frame, click on the labeling tab on the ribbon (which has few label tools), right click on the layer to get the full label properties.
Since I can't comprehend that this didn't make it into Pro from Map, looking forward to someone sharing where to turn this on in Pro.
Take a look at this post pertaining to Applying Advanced Symbology and Labeling Using ArcGIS Pro. It explains where a lot of items were moved and discusses a few key points such as the labeling view in the contents pane, labeling ribbon, label class pane, etc.