How can I access the attributes of a block within InnerBlocks?

Let’s say contains a core/gallery block inside which I want to render on my own. How can I get the gallery ID or the Image IDs in the server-side render.php?

block.js:

const { Gallery, InspectorControls, InnerBlocks } = wp.blockEditor;
const { registerBlockType } = wp.blocks;
const { Button, PanelBody, TextControl } = wp.components;
const ALLOWED_BLOCKS = ['core/gallery'];

const MY_TEMPLATE = [
    ['core/gallery', { placeholder: 'Gallery' }],
];


registerBlockType('my-gallery-block/main', {
    title: 'My Gallery',
    icon: 'dashicons-format-gallery',
    category: 'my-blocks',
    attributes: {
        htmlId: {
            type: 'string'
        },
        galleryIds: {
            type: 'string'
        }
    },
    edit({ attributes, className, setAttributes }) {
        

        return (<div>
            <div className="button-container">
                Gallery Block
                <InnerBlocks 
                    allowedBlocks={ALLOWED_BLOCKS} 
                    template={MY_TEMPLATE}
                    templateLock="all"
                    ></InnerBlocks>
            </div>
            <InspectorControls>
                <PanelBody
                    title="Settings"
                    initialOpen={true}
                >
                    <TextControl
                        label="HTML ID"
                        help="(optional)"
                        value={attributes.htmlId}
                        onChange={(content) => setAttributes({ htmlId: content })}
                    />
                    
                </PanelBody>
            </InspectorControls>
        </div>);
    },
    save() {
        return (<InnerBlocks.Content />);
    }
});

render.php:

<?php function render_gallery_block( $attributes, $content ) {


// How do I get the gallery ID or the Image IDs within the gallery?

 
ob_start(); 
?>
<?php 
    $output = ob_get_contents(); // collect output
    ob_end_clean(); // Turn off ouput buffer
        
    return $output; // Print output      
        
} 

I know that the $content variable already contains the rendered Gallery block as a HTML string, but I would like to avoid extracting the Image URLs from the HTML string if possible.

Does anyone know a better way?