Yoren Chang

Thanks to <a href="https://github.com/WebDevStudios/Taxonomy_Single_Term" rel="nofollow ugc">Taxonomy_Single_Term</a>, a library created by <a href="http://webdevstudios.com/" rel="nofollow ugc">WebDevStudios</a>, it made my work much easier on creating this plugin.
With Categories Metabox Enhanced, you can:
<ul>
<li>Change the built-in Categories metabox/panel to a single term UI, which means replacing the checkboxes with radio buttons or a select drop-down.</li>
<li>Apply the single term UI to other hierarchical taxonomies in the plugin’s Settings page.</li>
<li>Customized the single term UI by setting these options:
<ul>
<li>Priority and position of the metabox placement.</li>
<li>Title of the metabox.</li>
<li>If child-terms should be indenting.</li>
<li>If adding of new terms from the metabox is enable.</li>
</ul>
</li>
</ul>

Categories Metabox Enhanced

Replace the checkboxes with radio buttons or a select drop-down in the built-in Categories metabox and Gutenberg sidebar panel.

Ben Balter

This plugin will work, “as is”, out of the box, but assumes some level of CSS and developer customization to adapt to your site’s specific needs.
Styles can be overridden via your theme’s style.css
Functionality can be overridden via your theme’s functions.php
”Examples”
Don’t display metabox on “product” post type:
<pre><code>add_filter( 'display_custom_fields', 'bb_no_product_metabox' ); function bb_no_product_metabox( $true, $post ) { if ( $post->post_type == 'product' ) return false; return true; } </code></pre>
Don’t display the product_id metakey
<pre><code>add_filter( 'dcf_postmeta', 'bb_no_product_id' ); function bb_no_product_id( $postmeta ) { unset( $postmeta['product_id'] ); return $postmeta; } </code></pre>
Don’t display metabox title
<pre><code>add_filter( 'dcf_heading', '__return_false' ); </code></pre>
Display metabox below content (rather than floated to the right)
<pre><code>add_filter( 'dcf_before_content', '__return_false' ); </code></pre>

Display Custom Fields

Inserts a Wikipedia-like metabox into posts with all the post's associated custom fields and taxonomy terms.

Categories Metabox Enhanced vs Display Custom Fields