Question:

Where can I download the OneNote templates officially provided by Microsoft?
 

Answer:

In the early days of Microsoft, it should be that the OneNote 2016 was available for download from the official website.
OneNote is part of Office, so the OneNote template download location provided by Microsoft's official website is the same as the template download location of other Office applications, such as Word, Excel, PowerPoint.
By Office 2016, Microsoft had turned off template downloads for OneNote.
 
In Gem tab of "Gem for OneNote 2013,2010" -> "New" menu -> the " See Example Notebooks on Office.com" menu item is to jump to Microsoft's official website to download the OneNote template. The link is still a template that jumps to Office, but the OneNote template has been taken down.

Template download page of OneNoteGem.com.