Open Lightbox Image From Icon

can you show me a link to that page with the icon?

how did you insert the icon ( guess it is font-awesome) – as shortcode ?

or this way ?

<i class="fa fa-eye" aria-hidden="true"></i>

you can surround this with an <a href …></a>
see here your eye: https://webers-testseite.de/abc/

by the way – entypo-fontello got the eye too in the list – that is more comfortable to style.

https://www.w3schools.com/howto/howto_css_icon_buttons.asp

so again my question : how did you insert that icon

<a href="link to your image" ><i class="fa fa-eye" aria-hidden="true"></i></a>

I removed it from my page now – because i do not need font-awesome.

it remains visible in the frontend, but in the backend the code is unfortunately no longer visible after saving.
Maybe it is also due to my implementation via:

( just embedded via functions.php the fast way by:

function font_awesome_5(){
?>
  <link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.8.1/css/all.css" integrity="sha384-50oBUHEmvpQ+1lW4y57PTFmhCaXp0ML5d60M1M7uH2+nqUivzIebhndOJK28anvf" crossorigin="anonymous">
<?php
}
add_action('wp_head', 'font_awesome_5');