// Assigns a random style name to each image
function <MODULE_NAME>_views_pre_render(&$view)
{
  if($view->name == 'SOME VIEW')
  {
    $styles = array('thumbnail', 'medium', 'large');
    foreach($view->result as &$result)
    {
      $result->field_field_image[0]['rendered']['#image_style'] = $styles[array_rand($styles)];
    }
  }
}

function <MODULE_NAME>_views_pre_render(ViewExecutable $view)
{
  if($view->id() == 'SOME VIEW')
  {
    $styles = array('thumbnail', 'medium', 'large');
    foreach($view->result as &$result)
    {
      $image = $result->_entity->get("field_media_image");
      $image->SOME_FUNCTION('#style_name') = $styles[array_rand($styles)];
    }
  }
}

function <TEMPLATE_NAME>_preprocess_image_formatter(&$variables) {
  $styles = array('thumbnail', 'medium', 'large');
  if ($variables['image']['#style_name'] === 'medium') {
    $variables['image']['#style_name'] = $styles[array_rand($styles)];
  }
}