Disable native WordPress / browser lazy loading by adding class

disable_wp_lazyloading.php

//Disable native WP lazyloading for images by adding a CSS class lazyload-disabled  in Block Editor
//Now let's make the magic happen
add_filter('wp_img_tag_add_loading_attr', 'sz_disable_ll', 10, 3);
function sz_disable_ll($value, $image, $context){
    $disabled_class = 'lazyload-disabled';
    if (false !== strpos($image, $disabled_class)) {
        return false;
    }
    return $value;
}

//Now, in many cases you won't be able to add CSS class directly to the image, but it would be added to the Image block insted. Let's pass this value to the image inside the Image Block

add_filter('render_block', 'sz_disable_ll_inside_image_block', 10, 2);
function sz_disable_ll_inside_image_block($block_content, $block){
    if ('core/image' !== $block['blockName']) {
        return $block_content;
    }
    if (!empty($block['attrs']['className']) && str_contains($block['attrs']['className'], 'lazyload-disabled')) {
        
        
        $block_content = mb_convert_encoding($block_content, 'HTML-ENTITIES', "UTF-8");
        $document      = new DOMDocument();
        libxml_use_internal_errors(true);
        $document->loadHTML(utf8_decode($block_content));
        $imgs = $document->getElementsByTagName('img');
        if (count($imgs) > 0) { //if there are images in the content
            $img            = $imgs[0]; //get the 1st image
            $original_class = $img->getAttribute('class'); //get original classes to preserve it
            $img->setAttribute('class', (empty($original_class) ? 'lazyload-disabled' : 'lazyload-disabled ' . $original_class)); //whether class set up or not
            $block_content = $document->saveHTML();
        }
    }
    //Possible todo: add loading="eager" or/and preloading