Replace srcset

Replace.php

<?php


/**
 * add sizeSlug attribute where it is missing and update image src accordingly
 */

// alternative only for fixing sizeSlug:
// wp search-replace '(<!-- wp:image\s{(?!.*"sizeSlug")[^}]*)' '$1,\"sizeSlug\":\"full\"' gr8_posts --regex --regex-delimiter='/' --include-columns=post_content --log=C:\Users\Admin\Downloads\replace.log --precise

$posts = get_posts( ['post_type' => 'post', 'post_status' => 'publish', 'posts_per_page' => -1] );

echo 'Found ' . count($posts) . "posts\n\n";
foreach ( $posts as $post ) {
	// sizeSLug match: '/<!-- wp:image\s{(?!.*"sizeSlug")[^}]*/'
	// $matches[1] - id, $matches[2] - sizeSlug
	echo "Replacing in $post->post_title\n";
	$replaced = preg_replace_callback('/<!-- wp:image.*?"id":(\d+)[^"]*(?:"sizeSlug":"(.*?)")?.*?<!-- \/wp:image -->/s', function($matches) use ($post) {
		$sizeSlug_exists = isset($matches[2]);
		$image_size = $sizeSlug_exists ? $matches[2] : 'full';
		$new_image_url = wp_get_attachment_image_url( $matches[1], $image_size );

		$replacement = $sizeSlug_exists
			? $matches[0]
			: preg_replace('/([^}]+)/s', '$0,"sizeSlug":"full"', $matches[0], 1);

		$replacement = preg_replace('/(<img.*src=").*"/sU', "$1$new_image_url\"", $replacement);
		echo $replacement . "\n\n";
		return $replacement;
	}, $post -> post_content);
	$result = wp_update_post( ['ID' => $post->ID, 'post_content' => $replaced], true, false );
	if (is_wp_error($result)) {
		$errors = $result->get_error_messages();
		foreach ($errors as $error) {
			echo $error;
		}
	}
}