What does install button do from inside WP

I’m not sure what you mean but you do need to sync your Zotero accounts to use Zotpress even after installing the plugin.

While manual install and manipulation of files in WP directories was typical years ago, most plugins today can be (and I think most typically are) installed from inside WP by going to the plugin menu, searching, and clicking on the install button for the plugin from inside the WP gui.

Since your “help” files are not available until AFTER install, and you don’t explain whether a gui install resolves any requirement to fiddle manually with the directory, the question remains whether one has to manually fiddle the plugin AFTER the use of the install button from inside the WP gui (which is of course NOT the same as activating).

Additionally, the WP gui indicates that there is yet no confirmation of compatibility with the latest version of WP.

So, if one has the latest WP, clicks on plugins from inside the WP gui, searches for zotpress, and then clicks “install”, what exactly happens? Is what happens a complete install or does the user have to perform additional operations? And how does one implement the Zotero API key, i. e. does one need to create manually, at the Zotero.org website, a new key for zotfile (see e.g. the instructions here, which though better than the ones provided on the plugin site, fail to adequately address this) or is one supposed to use an existing key, and how does one see that key?

The same is true for Zotpress. I’m not sure if I understand the heart of the issue, but I did notice that I still have the “upload” instructions (WP provided this by default) on the Installation tab here, so I’ll add updating that to my to-do list. But actually I don’t think this 8+ year old plugin ever required manual install of the sort you mean. And when you install, like most modern plugins, Zotpress walks you through the few bits of additional setup.

Despite how easy (too easy in some cases) WP makes some things, a good rule of thumb is first installing on a development or local version of your website. But do let me know if there’s additional instructions needed or if something else is unclear.

The first item on the instalLation tab for the plugin when you search for and select the plugin from inside the WP GUI states, “Upload the folder zotpress to the /wp-content/plugins/ directory.” For most plugins, such instruction do not appear in the gui, as they are no longer necessary as the gui manages the install.

So, if the manual “upload” is no longer necessary from the gui, that should be clearly indicated.

Also, as I noted, there is still no info on what to do about the Zotero key.

OK…
So, I went ahead and clicked install, and then activate and all seems good.
Then I went into accounts and there were instructions as to how to validate yo my zotero account.