Add-on menu showing "Install" at the top of the list - What is it?

[Alan Wells]

After opening a Google Form that I had several add-ons installed in, and clicking the add-on puzzle icon, there was the "Install" menu item at the top.  I clicked on a different menu item and was prompted to install the add-on, which I did with no problem.  I don't know what this new "Install" menu item is?  Is it something related to the transition from the Webstore to the GSuite Marketplace?  Does it show up if the authorization is somehow no longer valid?  After I installed the add-on that I had already previously installed , the "Install" menu item disappeared.