This most likely applies to "plain" AutoCAD® and all verticals built on AutoCAD. The Start tab has been there for quite a few releases so far, but somehow I only figured the following out recently, so I thought I would document it here for anyone else who is unaware of it. I almost always start AutoCAD® Architecture from a desktop shortcut, and then start and leave open a blank, new drawing ("Drawing1"). This is an old habit - many releases back, settings would get lost if you closed the program in a "zero-doc" state (no open drawings), so I got in the habit of leaving the initial drawing that opened when starting the program from a shortcut (before the New/Start tab was added), as I like to save and close my working files manually, rather than relying on the program to prompt me to save any unsaved files if I were to close the program with working files open. (I have a lot of little habits like that - otherwise, I am perfectly normal.)
Anyway, now that the Start tab is there on startup, I usually create a new file from my default template, and had been using the Templates drop-down list to choose a template.
PS. Yes, I see the notification that I have three product updates. I checked, and they are for various versions of Revit®. I promise to download and install them soon.