Integer to Date in Nintex Forms

Hi guys,

I have an issue converting an integer to date in nintex forms.

Scenario:

I have a main list and a task list. Task Items are connected to the main item using Lookup Fields.

Using this formula I am able to get the latest DueDate of the task list for a specific main item:

This however converts the Date field to the integer representation of this field (e.g. "1624485600000").

I found the "convertToDate" and "formatDate" functions but unfortunately they tell me my value is not a number:

Normally you could convert this back to a Date for example using Javascript

var x = new Date(1624485600000)x.toDateString() //expected: "Thu Jun 24 2021"

 But using this, the form tells me this:

Last part translated: "The object does not support this action". This only occurs when I add the "new Date()" part to a calculated value in the form.

Is there any other way to convert this value back to a date?

I am using Forms for SharePoint 2013

Thanks!