There are some myths related to updating public apps on the Microsoft Store that I would like to dispel. I will demonstrate that public apps like RetroArch uploaded to the Microsoft Store can be updated, even if they are categorized as games.
For the purposes of this demonstration, an update to an existing public FTP app on the Microsoft Store will be shown. Note the app ID that is displayed for this existing app: 9P363P05BZLV. Also, note that it is categorized as a game.
Here's a screenshot of the app itself running on an Xbox.