Print Preprocessed username Field Value in User Template $account->getDisplayName() Bypasses "username" Field Preprocessing in User Template?

I am trying to print the value of the username field of the user account in a user--custom.html.twig file.

MYMODULE.module:

function hook_preprocess_user(&amp;$variables) {
  $account = $variables['elements']['#user'];
  $variables['userName'] = $account-&gt;getDisplayName();
}


user--custom.html.twig:

{{ user.name.0.value }}


Both the above examples access the username, but seem to access the value directly and circumvent any preprocessing of the username field (e.g. hook_preprocess_username()), so it looks like I need a different approach.

I have a view that shows the "User" entity so does not use fields and relies on the user template. What am I missing when trying to get the processed value of the username field, instead of the user name DB value for the account?

Related: Get username in custom user twig template but different.

In my template, I am rendering content.user_picture and trying to render username. So maybe I need to load the user instead of both fields? Looking for the processed username field value.
You're probably looking for the username theme:

$variables['userName'] = [
  '#theme' =&gt; 'username',
  '#account' =&gt; $account,
];