How is this used with Config Split?

I recently set up this module with config_split (note that this is a Drupal 10.1 site on the 1.x series of config_split, not 2.0 yet). It sounds like you have everything configured correctly. One tricky thing to remember: You might need to import config twice (e.g., drush config:import), once so that Drupal reads the new config-split settings, and the second to actually import that environment's split.

I second having to import the config twice, it's always drush cr; drush cim -y; drush cim -y.