By default this button doesn’t show. It will only come up if you have explicitly asked for it.
How are you generating the gallery? Have you written a shortcode for it? Or, are you using the Photonic Wizard to build it out. If you have written the shortcode, you have to ensure that you are not putting in any parameter called show_gallery.
If you are using the Wizard, you have to ensure that you are leaving blank the option that says “Show Gallery” button text. If you hover over that field, the documentation says, ‘Will show a “Show Gallery” button with the specified text. This will show a button instead of the gallery when the page loads, saving time on the load. Users can click on this button to see the gallery. Leave blank to show no button‘.