View Source Hello World Block Variation - A little rough around the edges. Tested successfully in the 2023 theme.

vs-block-variation.css

.wp-block-variation-hello-world {
	display: flex;
	background: #6fbcac;
    padding: 0 !important;
}

.wp-block-variation-hello-world .wp-block-group__inner-container {
    display: flex;
    gap: 1em;
}

.wp-block-variation-hello-world h3 {
    align-self: center;
    flex: 1 1 50%;
}

.wp-block-variation-hello-world .wp-block-image {
	display: block;
	flex: 0 0 50%;
  margin-block: 0;
}

.wp-block-variation-hello-world .wp-block-image img {
    display: block;
    width: 100%;
    height: 100%;
    object-fit: cover;
}

vs-block-variation.js

wp.domReady( function() {

    wp.blocks.registerBlockVariation(
        'core/group',
        {
            name: 'viewsource/block-variation-hello-world',
            title: 'Block Variation Hello World',
            icon: "admin-comments",
            category: "text",
            description: "a block variation",
            attributes: {
                className: 'wp-block-variation-hello-world',
                backgroundColor: 'secondary',
            },
            innerBlocks: [
                [ 'core/image', {
                    templateLock: 'all',
                    lock: {
                        move: "true",
                        remove: "true"
                    }
                } ],
                [ 'core/heading', {
                    level: 3,
                    templateLock: 'all',
                    lock: {
                        move: "true",
                        remove: "true"
                    }
                } ]
            ],
            isActive: (blockAttributes, variationAttributes) => {
            	// this does not appear to work and I don't know why
                return blockAttributes.className.includes("wp-block-variation-hello-world")
            }
        }
    );

});

vs-block-variation.php

<?php
/**
 * Plugin Name:     A Block Variations Demo
 * Description:     A response to https://viewsource.fm/s1/5
 * Author:          Mark Root-Wiley
 * Version:         0.1.0
 */

namespace MRW\BlockVariation;

add_action( 'wp_enqueue_scripts', __NAMESPACE__ . '\front_end_assets' );
function front_end_assets() {

	wp_enqueue_style(
		'vs-block-variation',
		plugin_dir_url( __FILE__ ) . 'vs-block-variation.css',
		array( 'wp-block-library' ),
		filemtime( plugin_dir_path( __FILE__ ) . 'vs-block-variation.css' ),
	);

}

add_action( 'enqueue_block_editor_assets', __NAMESPACE__ . '\block_editor_assets' );
function block_editor_assets() {

	wp_enqueue_style(
		'vs-block-variation',
		plugin_dir_url( __FILE__ ) . 'vs-block-variation.css',
		array(),
		filemtime( plugin_dir_path( __FILE__ ) . 'vs-block-variation.css' )
	);
	
	wp_enqueue_script(
		'vs-block-variation',
		plugin_dir_url( __FILE__ ) . 'vs-block-variation.js',
		array( 'wp-blocks', 'wp-dom-ready' ),
		filemtime( plugin_dir_path( __FILE__ ) . 'vs-block-variation.js' )
	);

}