Back in May 2022, I wrote about Sysvol Bloat with Group Policy ADM Template files.

I was removing the Office 2010 series of ADM Templates, as I’ve replaced them with the equivalent ADMX files, and ran into this issue:
Extra Settings – Word 2010 Default Document format

Delving a bit deeper, the Word14.adm Template specifies that if you select .docx, it would store “ “ as the value.  It writes this value into the Registry.Pol file.
The Word14.admx explicitly sets it as “.docx”.

So the solution was simple, in the Administrative Templates (ADMX) menu, explicitly set Word 2010 Default Format to  “.docx”.  Which then caused the Registry.Pol file to be updated with .docx, and removed the “Extra Registry Settings” settings.