Can Webchat Widget be opened by default without click the button?

The answer is yes, add the following script after the install code.

<script async defer src="https://www.uchat.com.au/js/widget/{YOUR_WIDGET_CODE}/float.js"></script>

<script>
window.addEventListener("chatbot:ready", function () {
    window.$chatbot.toggle('open');
});
</script>

Video Tutorial