SharePoint online document library metadata and Word quick part document property

Hi all,

I am trying to build a document management system in SharePoint online. I want to make it as easy as possible for the users and have certain requests from my customer.
They want you to put certain values in a pop-up windows when creating documents. It looks like I'll have to use Document sets unless I'm using PowerApps (which I don't know how to).

I would prefer to not use document sets because it is individual documents and it's annoying to have to go into the document set (folder) to see the files and also that the info box should not be opened all the time.

I have used both Term store and site content types in metadata columns and it works well.
But then we want to populate metadata and term sets in Word (to a header with columns as document standard templates) with quick parts -> document properties and that's when problems arise.

Two columns we want included in Word document properties from SharePoint are Created and Created by columns, but it seems that these two (and probably more) are built-in (system columns) and are not visible in Word document properties.
I tried a workaround and created a calculated column and chose in the formula that it should retrieve the Created by value, which went well, but calculated columns don't seem to work in Word document properties either. And Author in Word document properties does not work as it is not a SharePoint metadata.

Do you have any suggestions?

//T