by ishitaka on WordPress.org
XO Post Background is a plugin to set background image and color for each post.
Block Editor
Background image details (size, position, etc.) and background color can only be set in WordPress 5.7 or higher block editors.
Custom background images with parallax effect for posts, pages and products.
Set a featured image as the background for individual posts or pages with advanced options like parallax, overlays, and more.
This plugin provides a simple way to set an automatically scaled full screen background image.