You don't specify in you question what mechanism you are using to associate project document dependencies, but assuming you are using metadata of some sort on your document libraries to indicate which project(s) they are associated with, I think your best bet is to use the Highlighted Content WebPart:
In the settings of your WebPart instance, under the "Content" subheading, the "Source" dropdown allows you to choose to roll-up content from just the current site, or "All Sites", or "Specific Sites" (which then gives you a multi-select to choose which sites to get content from. Then you can choose the type of content to roll-up, such as Documents, Pages, or Images -- in your case, you want to choose "Documents". Then finally, you can use the "Filter and Sort" options to just get those documents whose project-dependency metadata matches your criteria. If the simple filtering isn't sophisticated enough for your metadata needs, you can always choose "custom query" at the top and write a full CAML or KQL query.