boa noite

<html>
    <style>
        .btn{
            color: purple;
        }
        .btn-active{
            background-color: red;
        }
    </style>
    <head>

    </head>
    <body>
        <button class="btn" onclick="toggle(this)">Teste 1</button>
        <button class="btn" onclick="toggle(this)">Teste 2</button>
        <button class="btn btn-active" onclick="toggle(this)">Teste 3</button>
        <button class="btn" onclick="toggle(this)">Teste 4</button>
    </body>
</html>

<script>
    const toggle = (e) => {
        let btns = document.getElementsByClassName('btn')

        for(let i = 0; i < btns.length; i++){
            btns[i].classList.forEach(element => {
                console.log(element)
                if(element == "btn-active"){
                    btns[i].classList.remove('btn-active');
                }
            });
        }
        e.classList.add('btn-active');
    }
</script>