WP plugin: ensure the Image block will omit extraneous elements when not resizable. E.g. inside a Gallery block.

image-block-filter.js

(({
	compose: { createHigherOrderComponent },
	element: { cloneElement, createElement: el },
	hooks: { addFilter },
}) => {
	const ImageInUnresizableContext = ({ blockEdit, blockEditProps: { context } }) => {
		// If resize is not allowed then the Image block should omit the element used to
		// limit the max width. Due to a bug it won’t, but it can be made to by adding a
		// `type` property to the `__unstableParentLayout` prop.
		if ( context.allowResize === false ) {
			const { props } = blockEdit;
			const { __unstableParentLayout: parentLayout } = props;
			// Take the type from `default.type` in the layout definition. Inside a
			// Gallery block this is currently 'flex'. Hardcoding the value could work
			// but given this could be running when the image is inside other blocks
			// there’s a chance that would cause breakage.
			const nextType =
				parentLayout.default?.type && { type: parentLayout.default.type };
			const nextProps = {
				...props,
				__unstableParentLayout: {
					...parentLayout,
					...nextType
				}
			};
			return cloneElement( blockEdit, nextProps );
		}
		return blockEdit
	}

	addFilter(
		'editor.BlockEdit',
		's8/image-in-unresizable-context',
		createHigherOrderComponent((BlockEdit) => (blockEditProps) => {
			const blockEdit = el(BlockEdit, blockEditProps);
			return blockEditProps.name !== 'core/image'
				? blockEdit
				: el(ImageInUnresizableContext, { blockEdit, blockEditProps });
		}, 'ImageInUnresizableContext')
	);
})(wp);

image-block-filter.php

<?php
/**
 * Plugin Name: Image block filter № 69566
 * Description: Ensures the Image block will omit extraneous elements when not resizable. E.g. inside a Gallery block.
 *
 * @package s8-image-block-filter-69566
 */

namespace s8\WP\ImageBlockFilter69566;

function hook() {
	wp_enqueue_script(
		's8-image-block-filter-69566',
		plugins_url( 'image-block-filter.js', __FILE__ ),
		array(
			'wp-compose',
			'wp-element',
			'wp-hooks',
		),
		filemtime( plugin_dir_path( __FILE__ ) . 'image-block-filter.js' ),
		true
	);
}

add_action( 'enqueue_block_editor_assets', __NAMESPACE__ . '\\hook' );