Sometimes all the pieces of the puzzle are just sitting there, but you can't see how they go together. And then you do. And you can't image how you didn't see it earlier.
Here's our problem. Clicking the Add To Table Button in the Map Layers and other Widgets won't automatically open that Table Widget we have in a Sidebar. Here's our puzzle pieces:
Do you see it? Here's the build.
- Starting with a Blank Fullscreen Template, we add a Sidebar Widget and set it to Full Size.
- In the Always Open Side, we put a Map and a Map Layers Widget.
- In the Collapsible Side, we put a Widget Controller.
- In the Widget Controller, we put a Table Widget.

- In the Widget Controller Settings, set the Widget Panel Arrangement to Fixed, the Width to 100% and use the Center-Bottom Square.

- In the Table Widget, chose Select Layers and then don't. ...Don't select any layers...unless you really want to.
- Set your Sidebar Widget with Resizable off, Default State Collapsed and Collapse Button off to make it unopenable.
The result:

Clicking Add To Table automatically triggers the hidden Widget Controller and opens the Table Widget. Users can close the Table with the X button or use the Arrows to minimize it, which isn't an option in ArcGIS Pro for some reason. It won't automatically un-minimize or prevent you from adding the same table twice, but all-in-all, I think it's a pretty slick presentation, maybe better than the Webmap Viewer or ArcGIS Pro.