Also found this

https://github.com/WordPress/gutenberg/issues/18272

this checks to see if a block is reusable, if I add this using code snippets would it be less resource intensive than your workaround?

function has_reusable_block( $block_name, $id = false ){
    $id = (!$id) ? get_the_ID() : $id;
    if( $id ){
        if ( has_block( 'block', $id ) ){
            // Check reusable blocks
            $content = get_post_field( 'post_content', $id );
            $blocks = parse_blocks( $content );

            if ( ! is_array( $blocks ) || empty( $blocks ) ) {
                return false;
            }

            foreach ( $blocks as $block ) {
                if ( $block['blockName'] === 'core/block' && ! empty( $block['attrs']['ref'] ) ) {
                    if( has_block( $block_name, $block['attrs']['ref'] ) ){
                       return true;
                    }
                }
            }
        }
    }

    return false;
}

I very slightly changed that to be

add_filter( 'baguettebox_enqueue_assets', function ($load) { return $load ?: is_singular(array('card', 'post' )); } );

so it works for posts and card type posts.

Still though, on card pages only the lightbox comes up, but not the image?

That doesn’t seem to have changed anything. The post does pull from an element within generatepress if that makes a difference, maybe the element (a content template) needs to be referenced too?