Drupal on Pantheon (upgrading to CKEditor 5)

Upgrade to Drupal 9.4.4 or higher.  For help with updates on Pantheon Composer driven sites, we have the following KB article.

Update modules providing additional CKEditor 4 plugins to the latest release of the major version you're on. Modules that have added CKEditor 5 support should provide support for both CKEditor 4 and 5, and provide an automated upgrade path (for toolbar items and plugin settings) from 4 to 5.

Enable the CKEditor 5 module (leave "CKEditor" module enabled) 

Converting text formats to use CKEditor 5

1. 1. Go to Text Formats ⮕ Editors in the Drupal Configuration user interface (usually under admin/config/content/formats) and click "Configure" for each text format.
   2. Under Text Editor change selection to "CKEditor 5" and click "Save configuration"
   3. Text formats must be updated one at a time. This will automatically migrate your text format configuration to CKEditor 5.
   4. Disable (old) "CKEditor" module.
   5. Note: This will change your configuration so make sure your export it.