Hi, this can be done with CSS. Here is a trick to output quick CSS for the field without enqueuing new CSS file:
<?php
add_filter( 'rwmb_meta_boxes', function( $meta_boxes ) {
$meta_boxes[] = [
'title' => 'Test Meta Box',
'fields' => [
[
'type' => 'file_upload',
'id' => 'test',
'name' => 'File Upload',
'after' => '<style>.rwmb-edit-media { display: none; }</style>'
]
],
];
return $meta_boxes;
} );