Error when using Smart Date widget on core Date range field

Problem/Motivation

Using the Smart Date and time range widget on a core Date range field returns an error and prevents the form from submitting.

Steps to reproduce

1. Create a new field using the Core date range field type
2. Set the form display to use the "Smart Date and time range" widget
3. Attempt to enter some content with a date.

An error is returned:

This value should be of the correct primitive type.

Tested in both Drupal 9.5.8 and 10.0.8 with Smart Date 4.0.0. It does not happen with version 3.7.2.