On-the-fly Invisible Halos
I've been creating what I call "invisible halos" for many years now. Every time I research a simpler way to accomplish what I want I am still amazed it isn't a built-in feature of ArcGIS Pro.
What I call an "invisible halo" is the same as a normal halo, but it is used to mask layers when there is more than one color behind the label or annotation. This is the case for the example above where the label for Saint Paul runs over two separately colored polygons. A single color, dynamically-updating label is not appropriate in this situation.
Instead what is needed is to follow a tedious process, and for each individual layer that has labels or annotations:
1) Turn on labels for you desired features and symbolize them appropriately
2) Convert the labels to annotations so they can be placed precisely where you want them
3) Run the Feature Outline Masks tool to create the halo that will be used as the mask
4) Turn off the newly created feature class
5) Click the checkbox(es) for the feature(s) you want to mask-out in order to let another layer through.
If for whatever reason an annotation needs to have its font, size, style, spacing, or other text characteristics updated the user needs to return to step 2 and do the whole process over again.
Applying a normal halo to labels has been available in ArcGIS Pro for nearly a decade. Why can't we have a feature that turns that halo into a mask?
If I were to create the feature I would list it in the Halo section of the Symbol tab on the Label Class pane. An option for the Halo symbol would be added for Invisible Halo. Once this option is chosen the resulting area below would expand to show checkboxes for layers the user would like to have masked with this newly created invisible halo.
This way the user can pan and zoom, have their labels dynamically update, AND mask out layers on-the-fly. This would be incredibly helpful to establishing the look of a published map, and even more so for those maps with an immense amount of detail.