Sure,
You can take the extension example code, even without fields. Just add a <form></form> in the template file.
add_filter( 'rwmb_meta_boxes', function( $meta_boxes ) {
$meta_boxes[] = [
'title' => 'Hero Content',
'id' => 'hero-content',
'description' => 'A custom hero content block',
'type' => 'block',
'icon' => 'awards',
'category' => 'layout',
'context' => 'side',
'render_template' => get_template_directory() . '/blocks/hero/template.php',
];
return $meta_boxes;
} );
template.php
echo '<div><form><button>Label</button></form></div>';
Using render_callback doesn't make a difference.
.
