When adding comment - gives website encountered error

Problem/Motivation

I am trying to add a comment but when saving the comment it gives me a website encountered error. This is related to getUsername() function.
Error: Call to undefined method Drupal\user\Entity\User::getUsername() in yg_flexy_preprocess_comment() (line 88 of /app/drupal9.5/themes/contrib/yg_flexy/yg_flexy.theme)