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Hi PinPointNetV,
In terms of your requirement, I’ve test it for multiple times, while there seems has no out-of-box way to make it, based on my test and experience, we are not allowed to combine with different document libraries, but as a workaround, I think you may use the Dynamic list filtering to filter the lists based on different document library webpart which might improve and also benefit your work efficiently, that’s why we suggest you use the feature of Dynamic list filtering.
Here are my steps: create a list (my sample is Filter with Policy, Invoices, Proposal) >add document webparts in your site Home page (for example, my sample is to add two document webparts because I have two document libraries named as "Documents & doc lib test)> set the Dynamic filtering as required>when I filter Policy in the Filter list> it can filter both document libraries as I want. See below screenshots:
For more details you can refer this article: Dynamic list filtering
We appreciate your patience and understanding again!
Best regards,
Gloria