Collector.ElementsInView running through multiple documents opened in the background

[SeanP]

That node is not looking at the Background documents but rather the open file. You will need to find a package or Python code to get you Elements/views of other documents.

Filtered element collector to get elements of category on view in docs

I don’t believe you can get elements from a linked model by using a view in the current document. The views need to come from the document used in the collector. You might be able to modify the Data-Shapes node GetLinkedElement.InHostViewAndCategory to work with your process though. I believe the node filters out elements within the bounding region of the view. Just use that node alongside the filtered elements from your current document.