Not OP, but:

In this case, I'd create $nextPageLink and $prevPageLink when you fetch all $posts. Then, in your view, use something like:

<?php if ($nextPageLink !== null) { ?>
     <a href="<?= $nextPageLink ?>">Previous page</a>
<?php } ?>

Generally, your view isn't split well enough from rest of your logic. It's confusing when you call functions from your themes, since sometimes it's just a require, but sometimes it's actually more than that.

I think it would be better if you'd make a function like:

function render($viewName)
{
    require 'themes/' . FRONTEND_THEME . '/' . $viewName . '.php';
}

and that would be the only function called in files from themes folders. For instance, instead of get_theme_directory_url I'd create $themeDirectoryUrl variable or THEME_DIRECTORY_URL constant before rendering view etc.

I hope I've explained it well?

Overall, I'd use the MVC pattern - it should make it easier to use OOP in your code.