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Thank you! No conditional logic or advanced location is used.
This is the JSON file: https://drive.google.com/file/d/1JIx95Pf9-LmOKwTmN8RHlRwg4fXo5xVC/view?usp=share_link

[SOLVED]

I forgot to do the basic thing: Save Permalinks. It works!

Thank you, Long!

So, if my field ID is pro_new_id and the field label is ID, then the code will look like:

add_action( 'rwmb_pro_new_id_after_save_field', function ( $null, $field, $new, $old, $post_id ) {
    $storage = $field['ID'];
    $storage->update( $post_id, $field['pro_new_id'], $post_id );
}, 10, 5 );

Is that correct? Does it matter that I made the field Read-Only? Sorry, I barely speak PHP.

Thank you!