I'm getting this warning: Deprecated: Required parameter $template_loader follows optional parameter $post_type in [...]/wp-content/plugins/meta-box-aio/vendor/meta-box/mb-frontend-submission/src/Post.php on line 21
This line has the issue, with the last parameter being required:
public function __construct( $post_type = 'post', $post_id = 0, $config = array(), $template_loader ) {
$this->post_id = (int) $post_id;
....
Are you using PHP 8 version? I suppose that this error notice displays when you update PHP version 7.4 to 8. Some PHP functions need to update to compatible with the new version.
.
