Hello,
Per Microsoft’s announcement on retiring the SharePoint Add-Ins, the Nintex classic forms are transformed to New Responsive Forms. Some users might have used the Nintex List Forms Online web part on SharePoint pages to show their SharePoint list form. Post conversion of classic form to new responsive form, the Nintex List Forms Online web part does not show the New Responsive form, and it still points to the classic form. As of now there is no compatible web part available to show the New Responsive web part and Nintex has posted an idea for voting here.
The alternative is to use the Embed web part on SharePoint online site pages. Enter the New Form url as https://yourorgname.sharepoint.com/Lists/ListName/NewForm.aspx (replace the letters in bold with your org name and list name).
You can also use the iframe tag in within the Embed web part as shown below, adjust the height and width per your needs.
<iframe src="https://yourorgname.sharepoint.com/Lists/ListName/NewForm.aspx" height="900" width="500"></iframe>
Thank you.
