Missing schema: system.rss:channel and system.rss:items.limit

This issue is being reviewed by the kind folks in Slack, #needs-review-queue-initiative. We are working to keep the size of Needs Review queue [2700+ issues] to around 400 (1 month or less), following Review a patch or merge request → as a guide.

With a new schema we will need an upgrade path to go forward.

These were removed in #2409413: Remove fields that do nothing from the "RSS publishing" settings form → and any existing config should have been cleared by system_post_update_delete_rss_settings. If needed, you can the update manually:

\Drupal::configFactory()->getEditable('system.rss')
  ->clear('channel')
  ->clear('items.limit')
  ->clear('langcode')
  ->save();