Charts don't work with saved String date

MongoDB Atlas MongoDB Charts
3

I do control the creation of the objects, but I am not sure why they aren’t already saved as Date type, here is the node.js code for saving Date() with mongoose 5.13.15:

 dbo.collection("users").updateMany(
   {
     accountEmail: ...,
   },
   {
     $set: {
       ...some other parameter...,
       lastModified: Date(),
     },
   },
 );

At no point is it turned into String. Where could this be happening?

And would you mind sharing how to automatically turn any String dates into Date on the Atlas side?