I found most of the information I was looking for

There is allegedly an "appimageupdate" client that a user can download, but the recommended practice is to just install a different version of the specific appimage, such as Krita, and then after testing it, delete the one that you do not want to keep.

And it does not hurt anything to keep both.

And there is something called "Firejail," allowing a user to run the appimage in a sandbox.   I have NOT yet researched that topic.

Again, feel free to correct me.

I think it would help a newbie, if a distro shipped with an appimage directory and a tiny game like "2048," and explain what all the hoopla is about.   The newbie could then delete the directory, if they wish.   Or the question could be asked during installation of the distro.