List of project documents in a library

Good morning.  

I am trying to populate a SharePoint List field with a list of project documents from a library.  Each time a document is added to the library and assigned to a project the list item for that project is updated.  Basically I have a list of projects for approval, one row per project.  There is a button with an approval flow attached.  I need to build a condition that a minimum set of 3 documents needs to be present before the button appears: Business case, Finance report and Project Charter.  There is a content type for the documents, one of the fields is a drop-down with the above document Types as well as others.

I have an approval flow with a filtered link on the project ID number to the project library that works well so want to see if I can use that but I just need a list of the document types.  They don't need to be hyperlinks to the document, just the document types in plain text.  Not sure of the best way to do this:  JSON formatting, SP formula or a flow?  Any ideas welcome.