How to remove the slow SQL_CALC_FOUND_ROWS from WP_User_Query and replace with standard COUNT() which is more performant.

override_wp_user_query.php

<?php
/**
 * Before sql query is generated, intercept `query_vars` and set `count_total` to false
 * to prevent `SQL_CALC_FOUND_ROWS` from being added to the sql query.
 * Also set our new `query_vars` attribute to true to track if count is required.
 */
add_action( 'pre_get_users', function($wpq) {
    if ( isset($wpq->query_vars['count_total'] ) && $wpq->query_vars['count_total'] ) {
        $wpq->query_vars['count_total'] = false;
        $wpq->query_vars['run_count'] = true;
    }
} );

/**
 * Here we have the `wp_user_query` object containing the generated sql query
 * We hook to this action to run our own `count` on the table depending on the value
 * of our custom `query_vars` attribute from above.
 * We run the extra query on the db and store it in the class variable `total_users`
 */
add_action( 'pre_user_query', function($wpq) {
    global $wpdb;
    if ( isset($wpq->query_vars['run_count']) && $wpq->query_vars['run_count'] ) {
        unset($wpq->query_vars['run_count']);
        $sql = "SELECT COUNT(*) $wpq->query_from $wpq->query_where";
        $wpq->total_users = $wpdb->get_var( $sql );
    }
} );