Get Image file system location in Drupal

I have some custom code to display some images, the method used is somethign like this

$image_url = ImageStyle::load('del_photo')->buildUrl('private://del-photos-cropped/Haglewhit_Feb22_1.jpg');

This produces a url like this

"https://mywebsite.url/system/files/styles/del_photo/private/del-photos/Haglewhit_Feb22_1.jpg?itok=ie69Z5G4"

However, when I do something like this, I get false indicating it can’t find the file.

Drupal::service('file_system')->realpath('private://del-photos-cropped/Haglewhit_Feb22_1.jpg')

What am I missing here, I’m a newbie to drupal so any help or guidance would be appreciated