Hi @Valerio_Merani ,
The issue that you were facing was likely due to the Node.js driver not supporting serverless instances yet (namely the lack of support for the loadBalanced configuration as pointed out by other community members).
We have just released version 4.1.0 of our Node.js driver, which supports serverless instances. You should now be able to upgrade your driver version to 4.1.0 and connect to your serverless instance!
You may separately have to wait for Mongoose to update their library in order to use Mongoose with serverless instances.
Hope this helps!
– Chris