deprecated method getUsername()

thanks Sergiu!
sure, i'll test it asap.

In the comments of getUsername() it says that there are 2 options: getAccountName() or getDisplayName()

  /**
   * Returns the unaltered login name of this account.
   *
   * @return string
   *   An unsanitized plain-text string with the name of this account that is
   *   used to log in. Only display this name to admins and to the user who owns
   *   this account, and only in the context of the name used to log in. For
   *   any other display purposes, use
   *   \Drupal\Core\Session\AccountInterface::getDisplayName() instead.
   *
   * @deprecated in Drupal 8.0.0, will be removed before Drupal 9.0.0.
   *   Use \Drupal\Core\Session\AccountInterface::getAccountName() or
   *   \Drupal\user\UserInterface::getDisplayName() instead.
   *
   * @see https://www.drupal.org/node/2572493
   */
  public function getUsername();

I've implemented hook_user_format_name_alter() and changed how the username looks wherever it's displayed. getAccountName() is ignoring that hook and just displays the username field.

Long story short, let's use getDisplayName() instead

Thank you @sergiu-stici!