You have likely upgraded Drupal to version 10.3.0 and noticed a new message in the reports regarding the State Cache:
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The message reads as follows:
The State Cache flag $settings['state_cache'] is not enabled. It is recommended to enable it in settings.php unless too many keys are stored. Starting with Drupal 11, State Cache will be enabled by default.
What is the State API?
Let's begin by understanding what the State API is. The State API in Drupal is a system that allows the storage and retrieval of small data fragments that are necessary for site operation but are not part of the overall configuration. Unlike the Config API, which focuses on data that must be consistent across different environments (like production, development, etc.), the State API is intended for environment-specific data that can change more dynamically and do not need to be synchronized across different environments.