Reply To: required fields

Ah, if you want to keep the email field, then in the 2nd snippet, it's available in the $data, so you should keep it (e.g. don't assign it to a completely new array).

The 2nd snippet should be:

add_filter( 'rwmb_profile_insert_user_data', function ( $data, $config ) {
    // User strpos because the $config also contains default register form.
    if ( false === strpos( $config['id'], 'user-account' ) ) {
        return $data;
    }
    // Custom data for user.
    $data['user_login'] = 'my_user3';
    $data['user_pass']  = 'my_user_pass';
    return $data;
}, 10, 2 );