Gary Jones

This plugin adds a Visual Subtitle field to all post, page and custom post types that have support for a title, and that use the Classic Editor. It doesn’t work with the Block Editor.
It allows you to include a string of text that will still be part of the post title, but be wrapped in a <code>span</code> tag, giving something like:
<pre><code><h1>Visual Subtitle</h1>
</code></pre>
Keeping it as part of the main level 1 or two heading, means it maintains as much keyword SEO importance as the main title, yet can be given a style (in your own theme) of <code>display: block;</code> to make it visually appear as a subtitle.
The visual subtitle is appended to to the title on on the Posts screen, separated with a pipe (<code>|</code>) character, and appended to the title part of the document title with a colon (<code>:</code>) character.
<h3>Translations</h3>
<ul>
<li><a href="http://deckerweb.de/material/sprachdateien/wordpress-plugins/#visual-subtitle" rel="nofollow ugc">Deutsch</a></li>
</ul>

Visual Subtitle

Allows part of a post title to be styled as a subtitle. It is still within the title heading, but is wrapped in a span to be styled differently.

Suzanne

For Genesis child themes that output HTML5 only.
This plugin adds an entry field just below the title field on all post, 
page and custom post type edit screens. It allows you to specify a 
subtitle for the content and then outputs the result in an H2 tag just 
under the entry-title where you’d expect to find it.
This plugin is for use with Genesis HTML5 child themes only because it 
uses the hook, genesis_entry_header to position the output after the 
title but before the post-info.

Genesis Subtitles

For Genesis child themes that output HTML5 only.

Visual Subtitle vs Genesis Subtitles