With PowerPoint 2010, there was the ability to autoload templates with the .PPAM extension, by deploying the template to %ProgramFiles%\Office14\ADDINS\ and it would load with the launch of PowerPoint.
When migrating to PowerPoint 2016 however, this doesn’t work. Of course you’ll need to change the folder from Office14 to Office16, but it will still ignore the .PPAM template file.
The fix, I eventually found after trying several things, was to just rename the file from .PPAM to .POTM – no need to open and resave the file, just rename the file itself.
I can’t find anything specific about this online, but it works.
Side note – Excel and Word 2016 templates works the same way as 2010, with the XLSTART and STARTUP folders respecively for XLAM and DOTM templates.
(Updated to .POTM rather than .POTX for the file extension, as .POTM is macro enabled while .POTX is a template without macros – thanks Rhys!)