how to fix issue on tampermonkey script

Try to use ` ... ` ;
You can search about template string in javascript.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_literals

document.onkeypress = async function(e) {
        e = e || window.event;
        var charCode = (typeof e.which == "number") ? e.which : e.keyCode;
        if (String.fromCharCode(charCode) === '=') {
            const {
                value: formValues
            } = await Swal.fire({
                title: 'Enter your credentials ',
                html: `<input id="swal-input1" class="swal2-input" placeholder="email" type = "text" value = "[email protected]" >
                       <input id="swal-input2" class="swal2-input" placeholder="password" type = "password" value = "A23@" > `,
                focusConfirm: false,
                preConfirm: () => {
                    return [
                        document.getElementById('swal-input1').value,
                        document.getElementById('swal-input2').value
                    ]
                }
            })

Also, you can try like below;

html: '<input id="swal-input1" class="swal2-input" placeholder="email" type="text" value="[email protected]"> <input id="swal-input2" class="swal2-input" placeholder="password" type="password" value="A23@" > ',