[SOLVED] hook_ENTITY_TYPE_presave() not working

I'm working on a custom module to update a field "curryear_birthdate" in an entity "Person" in my Drupal 10.2.4 site using the hook_ENTITY_TYPE_presave() construct.  I followed the template that several Drupal guides showed.

I have two problems:

1) The field doesn't get updated; and
2) I put a debugging display in to see what might be the problem and the display is not appearing.

The code for the .module is shown below.

<?php

use Drupal\Core\Entity\EntityInterface;

/**
 * Implements hook_ENTITY_TYPE_presave() for person entities.
 */
 
echo '<script>alert("Got into birthdaycurryear.module")</script>'; 
function curryear_birthdate_Person_presave(Drupal\Core\Entity\EntityInterface $entity) {
   echo '<script>alert("Got into curryear_birthdate_Person_presave function")</script>'; 
  if ($entity_type->get('type') === 'Person' && $entity->hasField('Birthdate of person')) {
    $birthdate = $entity->get('Birthdate of person')->date;
    $dateAsStr = $birthdate->format('Y-m-d-H-i-s');
       echo '<script>alert("Birthdate = ".$dataAsStr)</script>'; 
    if ($birthdate) {
      $current_year = date('Y');
      $month = $birthdate->format('m');
      $day = $birthdate->format('d');
      $curryear_birthdate = new DateTime("$current_year-$month-$day");
      $entity->set('curryear_birthdate', $curryear_birthdate->format('Y-m-d'));
    }
  }
}

The first display [echo '<script>alert("Got into birthdaycurryear.module")</script>'; ] works fine.  Every time I do a step the pop-up display shows, so I know that the system knows that my module is around and installed.

But, my second display [echo '<script>alert("Got into curryear_birthdate_Person_presave function")</script>'; ] never shows.

I anticipated that any time I tried to update a Person record that second display would show, but it never does.

So, either:

1) echo displays within functions don't work the way I think they would;
2) The system never triggers the curryear_birthdate_Person_presave() function; or
3) There's a syntax error that the system is not telling me about

I usually assume that I'm missing something simple.
I'd appreciate anyone telling me what that "something simple" might be in this case.

Thanks!