At MidCamp a few weeks ago, Martin Anderson-Clutz tapped me on the shoulder to check out a Smart Date issue for compatibility with Drupal 10.2. As of Drupal 10.2, ListItemBase::extractAllowedValues takes an array as its first argument versus a string. The method used to explode a newline separated string into an array for its callers. I took a look at the issue. The change affected the parseValues method in the SmartDateListItemBase class. The parseValues method takes the field's values and passes them to extractAllowedValues, the method with a changed signature in Drupal 11.
The original method contained the following:
PubDate