Sio

Using a link is the correct way to link directly to a product detail page from the navigation.
As you said, you can link directly to the product by pasting the full url. Note that you should avoid including the first part of the url (the part containing the domain), so that the link is just "/prints/p/productname".
You can hide the link by dragging it from MAIN NAVIGATION to NOT LINKED within the Pages panel.
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Moving the whole additional info up under the image might be problematic as that area wasn't designed to have extra stuff put in there. It is easier to move blocks out of AI to other places. The only place I've done it is into the detail area as that was designed to be somewhat flexible in accepting new elements.
If you need just one phrase below the images you could use something like the following.
Add the following to Store Settings > Advanced > Page Header Code Injection for the store page. Please see per-page code injection.
<style> .ProductItem-gallery::after { content : 'Click to show the full image'; order : -1; } </style> This is for v7.1.
It could be wrapped in a media query if you only want it to appear on mobile.

Awesome, thanks! I'll be testing this out. Even if I don't use it now, it might be useful for the future.
Most importantly, many thanks for the plugin, creedon! Sent you a small donation just now, because without the plugin we literally would not have been able to launch our website earlier today; the 'Click to enlarge' text was that important. 🥳 Please keep up the great work!