How do I trigger a lightbox in URL that contain utm query parameter?

Keep in mind that wixLocation.query returns an Object . The code you want is something like this:

    let query = wixLocation.query;
    console.log('query', query); // inspect the returned query Object
    if(query.utm === 'facebook') {
        wixWindow.openLightbox("LightboxName");
    }
    else {
        // something else if utm is not "facebook"
    }