Look at the videos again. In neither of them did the document open with a file extension after the Document#!
If you OPEN the dotm,

it is the template itself that you are opening and as a result it shows the name of the template IR-Shoulder.dotm and if you make any changes and then click on Save, those changes will be made to the template itself, which would normally not be the desired result. If you use FIle>Save As, the file type will be Word Macro-Enabled Template (*.dotm) because that is the type of file. It will not be *.docm or *,docx, regardless if one of those types is set as the default under File>Options>Save.

However, the default double click action for a template is that shown in bold font - New and if you click on New or double click, the document that appears on the screen with the Document# That document is created from the template and contains a reference to the template so that the code in the template is available for use with that document.

WORD HAS WORKED THIS WAY FOR THE LAST 25 YEARS AT LEAST!