Get Current Applied Image Style Name
Field format display options are components of view modes, stored in the config entity EntityViewDisplay.

For example, load the default view mode for the user and extract the configured image style of the user_picture field:

use Drupal\Core\Entity\Entity\EntityViewDisplay;

  $component = EntityViewDisplay::load('user.user.default')-&gt;getComponent('user_picture');
  $image_style = $component['settings']['image_style'];