Last week I wrote up a walkthrough in dealing with a change introduced for List field validation in Drupal 10.2 using a stored procedure to rewrite existing data. After some discussion, this change has been reverted in an upcoming patch release for Drupal 10.2:
Regression from #2521800: using machine name element for ListStringItem breaks with existing data
You can apply the patch from the issue to Drupal 10.2.0, or wait for the patch release before upgrading. Thanks to the core team for their fast work on this!