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.

GTPlugins

Search Taxonomy GT makes it easier for you to search for your taxonomy terms in the backend when inserting/editing posts on your wordpress website.

Search Taxonomy GT

Search Taxonomy GT - This plugin adds a functionality inside the taxonomy metabox when inserting/editing posts for live taxonomy term search.

Categories Metabox Enhanced vs Search Taxonomy GT