Every time I hit Enter It updates in the same tag
First I sent Hello World!
The second time I tried to send Hello as a new message It was updated with the same tag

I have only provided chunks of code which is being used for this send msg functionality

This the code I am also using speech to text which is why I have used setTranscriptValue to set speech value inside textarea

handleKeyDown function is called onKeyUp in textarea

const [sendMsg, setSendMsg] = useState(<p></p>);

const handleKeyDown = (event) => {
        console.log(event);
        setTranscriptValue(event.target.value.trim());
        if (event.key == 'Enter') {
            handleSendKey();
            setTranscriptValue('');
        }
    };

const handleSendKey = (event) => {
        setSendMsg(<p> {transcriptValue} </p>);
    };

<span id="send-btn" className='material-symbols-outlined' onClick={handleSendKey}> send </span>

<ul className="chatbot__box" id="ul-chatbot-box">
                    <li className="chatbot__chat incoming" id="li-incoming-msg">
                        <span className="material-symbols-outlined">
                            smart_toy
                        </span>
                        <p>Hi there, How can I help you today?</p>
                    </li>
                    <div
                        id="div-btn-res"
                        className="btn"
                        style={{ display: 'none' }}
                    ></div>
                    <li className="chatbot__chat outgoing"> {sendMsg} </li>
                </ul>

>Solution :

If you want to grow a list of messages, you should maintain an array instead of a single element.

It’s also not recommended to store JSX elements in state. Store data only and leave the rendering to the component.

const [sendMsg, setSendMsg] = useState([]); // init with an empty array

const handleSendKey = (event) => {
  setSendMsg((msgs) => [...msgs, transcriptValue]); // add to the array
};

Then in your render / return value, map over the values

{sendMsg.map((msg, i) => (
  <li className="chatbot__chat outgoing" key={i}>
    <p>{msg}</p>
  </li>
))}