Quotes not rendering properly in WooCommerce settings API [closed]

You’re creating a string representation of an array, when you need an actual array!

$blogusers = get_users();
$options = array();

foreach ( $blogusers as $user ) {
    $options[ $user->user_email ] = $user->user_email; // No need to pass through __(), don't translate emails!
}

And then pass it to your options argument:

$this->form_fields = array(
    'sec_r2_mail' => array(
        'options' => $options,
        // Other arguments
    ),  
);