您可以使用get_the_category() 并返回第一个结果，如示例所示。从技术上讲，您可能有多个父类别，因此需要单独处理，或者期望数组的第一个元素始终是正确的父类别。

粘贴此代码single.php 根据您的主题风格

$cats=get_the_category();
    foreach($cats as $cat){
/*check for category having parent or not except category id=1 which is wordpress default category (Uncategorized)*/
        if($cat->category_parent == 0 && $cat->term_id != 1){
            echo \'<h2 class="link"><a href="\'.get_category_link($cat->term_id ).\'">Return</a></h2>\';
        }
        break;
    }

<h2 class="link"><a href="(Link to first category which not have any parent category)">Return</a></h2>

<h2 class="link"><a href="<?php $cat = get_the_category(); $cat = $cat[0]; echo get_category_link($cat->cat_ID); ?>">Return</a></h2>

This should work!