add hidden radio buttons with Value=1 and default check in yours html

radiobutton_check.js

// 9
function Ninth() {

    let question1Value = +document.querySelector('input[name="que1"]:checked').value,
        question2Value = +document.querySelector('input[name="que2"]:checked').value,
        question3Value = +document.querySelector('input[name="que3"]:checked').value,
        result;

    if (question1Value === 1 || question2Value === 1 || question3Value === 1) {
        modalo();
        document.getElementById('result-ninth').value = 'Сделайте выбор , пожалуйста!';
        return 0;
    } else {
        result = question1Value + question2Value + question3Value;
        switch (true) {
            case (result === 6):
                document.getElementById('result-ninth').value = 'Вы набрали ' + result + ' балов , Молодчинка!';
                break;
            case (result === 4):
                document.getElementById('result-ninth').value = 'Вы набрали ' + result + ' балов , Можно и лучше!';
                break;
            case (result === 2):
                document.getElementById('result-ninth').value = 'Вы набрали ' + result + ' балов , Мда...!';
                break;
            case (result === 0):
                document.getElementById('result-ninth').value = 'Вы набрали ' + result + ' балов , Это печально...!';
                break;
            default:
                document.getElementById('result-ninth').value = 'Что-то пошло не так...';

        }
        modalo();
    }

    function modalo() {
        $('#open-door').click(function () {
            $('.modal-wrap').fadeIn();
        });
        $('.close-me').click(function () {
            $('.modal-wrap').fadeOut();
        });
    }
};

/* some HTML */

 <div class="questions">
            <h3> "2"+ 2 = ?</h3>

            <div class="row">
                <input type="radio" id="que3-s1" name="que3" value="0">
                <label for="que3-s1">4</label>
            </div>
            <div class="row">
                <input type="radio" id="que3-s2" name="que3" value="0">
                <label for="que3-s2">"2"2</label>
            </div>
            <div class="row">
                <input type="radio" id="que3-s3" name="que3" value="2">
                <label for="que3-s3">22</label>
            </div>
            <label class="d-none"></label>
            <input type="radio" class="d-none" name="que3" value="1" checked>
        </div>