tantive

This plugin allows background images to be set for all blocks. 
You can set CSS background-image, background-repeat, background-attachment, background-position-x, background-position-y, and background-size.

Tantive Set Background

Example block scaffolded with Create Block tool.

Anil Sardemann

This plugin distinguishes between block and non block themes to add a fullscreen background image to WordPress. It is set either to the body tag (in case of a non block theme) or to the wp-site-blocks class (in case of a block theme). Upload an image or choose one from your media library. Simple plugin that allows you to set a background image for your website easily.
<a href="https://playground.wordpress.net/?plugin=custom-background-image" title="WordPress Playground Demo" rel="nofollow ugc">Demo</a>

Custom Background Image

Simple plugin that allows you to set a background image easily. Upload an image or choose one from your media library.

Tantive Set Background vs Custom Background Image