Limit exposed filter options.

contacts.js

(function($, Drupal) {
  'use strict';

  Drupal.behaviors.viewContactContacts = {
    attach: function(context, drupalSettings) {

      // List of tids from pacificsource_preprocess_views_view__contact_contacts().
      const $tids = drupalSettings.pacificsource.view_contact_contacts.contact_tids;

      // Target the correct view.
      const $view = $('.view-contact-contacts');

      if($view.length > 0) {
        $view.find('option').each( function(){

          // Remove options not included in the $tids array.
          if (!$tids.includes($(this).val()) && $(this).val() != 'All' ) {
            $(this).remove();
          }
        })
      }
    }
  };
})(jQuery, Drupal);

gistfile1.txt

x

view.php

/**
 *  * Implements hook_preprocess_views_view__NAME().
 */
function pacificsource_preprocess_views_view__contact_contacts(&$variables) {

  $variables['#attached']['library'][] = 'pacificsource/view_contact_contacts';

  $tids = [];

  /** @var \Drupal\views\ViewExecutable $view */
  $view = $variables['view'];
  $results = $view->result;

  // Get tids from from field_insurance_type.
  foreach ($results as $result) {

    /** @var Drupal\node\Entity\Node $node */
    $node = $result->_entity;

    $taxonomy_values = array_merge(
      $node->field_contact_role->getValue(),
      $node->field_counties->getValue(),
      $node->field_insurance_type->getValue(),
      $node->field_region->getValue(),
      $node->field_state->getValue(),
    );

    foreach ($taxonomy_values as $taxonomy_value) {
        if (!(in_array($taxonomy_value['target_id'], $tids))) {
          $tids[] = $taxonomy_value['target_id'];
        }
    }
  }

  // Send tids to drupalSettings so they're available for use in js.
  $variables['#attached']['drupalSettings']['pacificsource']['view_contact_contacts']['contact_tids'] = $tids;

}

Because the filter is rendered before the view has results I decided to get the tids from the results then send them to js via drupalSettings. Then I removed the unneeded filter options via js.

Would have been better to get all terms instead of listing each field.