Pagination row shows all pages when applying tag

Hi,

When I apply the tag !–nextpage–> on specific pages where i want the text to be split, it shows the whole row of pages counting, which it is not practical, for example on the page example I am sharing you can see the whole 35 page breaks number in a row, and I wanted something short like “First – groups of five pages – Next or Previous. I have tried several changes in the code but, none apply to it. I am guessing maybe I am not applying the changes in the correct files, so far I have tried in the functions.php, index.php and navigation.php following some solutions I came across online. I also have the WP Page Navi plugin, but, not doing anything. Basically, I wanted a simple solution that could provide the display of the row as I’ve stated “First – groups of five pages – Next or Previous” something along those lines. I don’t know if it is also possible to achieve it through custom CSS, so any solution will be much appreciated. Here’s the example: https://www.popexpresso.com/pop-expresso-videos-music/

Thanks,

David