This plugin allows you to add and image as background of posts, pages or custom post type in general (in the same way as a thumbnail).
<ul>
<li>This is a rewrite of my old plugin <a href="https://wordpress.org/plugins/post-background/" rel="ugc">Post Background</a> which I do not have access anymore. *</li>
</ul>

WP Post Background

This plugin allows you to add and image as background of posts, pages or custom post type in general (in the same way as a thumbnail).

ishitaka

XO Post Background is a plugin to set background image and color for each post.
Background image details (size, position, etc.) and background color can only be set in WordPress 5.7 or higher block editors.

XO Post Background

XO Post Background is a plugin to set background image and color for each post.

WP Post Background vs XO Post Background