I am not really sure where you want the text in the page you linked to, but I can tell you how to hide it on Single post page so that could can simply add it in the post content wherever you like.
Do do that, add the HTML below wherever you want in your post content (using the TEXT view if using the classic editor, or an MTML block if using the block editor.
<div class="mytext">Type your text here</div>
Then just add the CSS rule below to your theme Global Custom CSS Rule box.
.mytext {display:none;}
.single .mytext {display:inline-block;}
Once the principle works, we can work on more styling rules to fine tune the style of that content