The code will redirect visitors from desktop devices but not for a specific user. Change the $my_ip to your own IP.

redirect-desktop-users-except-for-specific-users.php

<?php

// Redirect mobile visitors to your desktop site
function wimtec_mobile_redirect() {
    
    // My IP
    $my_ip = '90.22.192.117';

    // Get the client IP
    $client_ip = $_SERVER['REMOTE_ADDR']?:($_SERVER['HTTP_X_FORWARDED_FOR']?:$_SERVER['HTTP_CLIENT_IP']);

    if( $client_ip === $my_ip ) {
        return false; exit;
    } else {
        if( ! wp_is_mobile() )     {
            wp_redirect('https://wimtec.net');
            exit;
        } 
    }
}

add_action('init', 'wimtec_mobile_redirect');