Where do Word for Mac and Powerpoint for Mac store user templates?
In the English version of Word and PowerPoint 2011, Templates are stored inside your Home folder in
~/Library/Application Support/Microsoft/Office/User Templates/My Templates. In other languages, the
User Templates/My Templates part is localized (e.g.
Benutzervorlagen/Eigene Vorlagen/ in German).
The User's Library folder is hidden in 10.7 and later, but you can go there by holding down option while clicking the Go menu in the Finder, then selecting Library.
According to this page, and confirmed by experiment, the path has changed for Office 2016. It is now
~/Library/Group Containers/UBF8T346G9.Office/User Content/Templates. (This is what you see in the Finder: if you use Terminal the last two directories have ".localized" appended to their name, which Finder evidently suppresses).
Be aware that if you performed an upgrade of Office, you will still have the
~/Library/Application Support/Microsoft/Office/User Templates/My Templates directory, but Powerpoint, at least, won't look in that location.
The location changes with newer Microsoft Office versions for Mac. The location for my MacBook Pro 2021, using Microsoft Office 365, matches that from TechnoCat's comment under Dave Mulligan's answer.
/Users/[your_username]/Library/Group Containers/UBF8T346G9.Office/User Content/Templates].
The location is normally invisible, so you will need to reveal hidden files to find it. There's more than one way to do this. The easiest is simultaneously pressing
cmd + shift + .. Using Terminal:
defaults write com.apple.Finder AppleShowAllFiles true killall Finder
And then to hide the files again:
defaults write com.apple.Finder AppleShowAllFiles false killall Finder