Required file fields are not programmatically identified for assistive technology.

If you need a workaround for this issue, then you can put this in your custom theme:

/**
 * Implements hook_element_info_alter().
 */
function MY_THEME_element_info_alter(array &$info) {
  $info['managed_file']['#process'][] = '_MY_THEME_process_managed_file_element';
}

/**
 * Processes managed file elements.
 *
 * A required attribute isn't set on the child upload element and it can't be
 * done in a preprocess function. It must be set before the element is
 * rendered.
 *
 * @param array element
 *   A managed file form element.
 *
 * @return array
 *   The processed managed file element.
 *
 * @see https://www.drupal.org/project/drupal/issues/2852874
 */
function _MY_THEME_process_managed_file_element(array $element) {
  if (isset($element['#required']) && $element['#required']) {
    $element['upload']['#required'] = TRUE;
  }
  return $element;
}

I'll see about fixing it properly in Drupal Core another time.

Tagging for initial review with the accessibility team.
I'll work on issues depending on the inputs from the team.

I'm in favour of using "aria-required: true" unless there aren't any other ways.

Currently when field is required, we have following markup in claro in standard profile.

I do want to make sure that we are building on well researched patterns. There are a few like:

• https://www.w3.org/WAI/WCAG21/Techniques/aria/ARIA2
• https://www.tpgi.com/doing-whats-required-indicating-mandatory-fields-in...
• https://www.digitala11y.com/anatomy-of-creating-accessible-forms-is-this...

This is a common problem and we should be able to leverage a pattern which is both well tested and well established.