How do I export a list of users into an excel spreadsheet in Drupal 9

Assuming you are willing to use drush: Create a PHP script, named something like users_to_csv.php

<?php

$fields = [
            'name',
            'mail',
            'langcode',
            'preferred_langcode',
            'timezone',
            'created',
            'changed',
          ];

$users = \Drupal::entityTypeManager()
            ->getStorage('user')
            ->loadByProperties([
              // some properties here if you care to restrict the users list
            ]);

foreach ($users as $user ) {

  foreach ($fields as $field) {

    echo $user->get($field)->getValue()[0]['value'] . ', ';

  }

  echo PHP_EOL;

}

Then run it with

drush php:script users_to_csv.php > users.csv

The fields list is up to You.