Search Filter by first and last name and by user ID

user_prop__multi_search.php

<?php
add_filter( 'jet-smart-filters/query/final-query', function( $query ) {
    if ( empty( $query['meta_query'] ) ) {
        return $query;
    }

    foreach ( $query['meta_query'] as $index => $meta_query_item ) {
        // Check for our custom marker key (e.g., user_prop__multi_search)
        if ( isset( $meta_query_item['key'] ) && false !== strpos( $meta_query_item['key'], 'user_prop__multi_search' ) ) {
            $search_value = $meta_query_item['value'];

            // 1. Configure search by standard database columns (including ID)
            $query['search'] = '*' . $search_value . '*';
            $query['search_columns'] = array( 'ID', 'user_login', 'user_nicename' );

            // 2. Add search by metafields (first_name and last_name) using OR relation
            $query['meta_query'][] = array(
                'relation' => 'OR',
                array(
                    'key'     => 'first_name',
                    'value'   => $search_value,
                    'compare' => 'LIKE',
                ),
                array(
                    'key'     => 'last_name',
                    'value'   => $search_value,
                    'compare' => 'LIKE',
                ),
            );

            // Remove the temporary marker so it doesn't break the main query
            unset( $query['meta_query'][$index] );
        }
    }

    return $query;
} );