Hi,
I have share the HTML code of the LP and attached the Form Field (Last Name) and Alert Message for [Object.Object].
<html>
<head>
<title>My Test LP</title>
</head>
<body>
<script src="//*******.mktoweb.com/js/forms2/js/forms2.min.js"></script>
<form id="mktoForm_1234">
</form>
<script>MktoForms2.loadForm("//*****.mktoweb.com", "******", 1234);</script>
<script>
function unrequireField(mktoForm, fieldName, options = {}){
const defaultOptions = {
alsoHide: false
};
options = Object.assign(defaultOptions, options);
const formJq = mktoForm.getFormElem();
const fieldJq = formJq.find(`[name="${fieldName}"]`);
if(!fieldJq.length) {
return;
}
const fieldRowJq = fieldJq.closest(".mktoFormRow");
const fieldWrapperJq = fieldJq.closest(".mktoFieldWrap");
const fieldDescriptorJq = fieldJq.closest(".mktoFieldDescriptor");
fieldJq.removeAttr("aria-required");
fieldJq.removeClass("mktoRequired");
fieldWrapperJq.removeClass("mktoRequiredField");
fieldDescriptorJq.data("mktoFieldDescriptor").required = false;
if(options.alsoHide){
fieldRowJq.hide();
}
};
MktoForms2.whenRendered(function(renderedForm){
unrequireField(renderedForm, "LastName", {alsoHide: true});
alert("renderedForm==="+renderedForm)
});
</script>
</body>
</html>

It’s frustrating to have to create a demo page because you won’t provide one. But here’s that exact code running fine: https://cdpn.io/pen/debug/abxoeGr/0bc39e6798134d52fab1879867b28185.
There’s no issue with the code. [object Object] is the default toString() output for a JS Object. The LastName field is hidden as expected.