Installation and configuration of CKEditor 5 module on Drupal 9

CKEditor 5 is included in Drupal 9.3 as an experimental module. To use it, install it and switch existing text formats to use CKEditor 5. Text formats that were using CKEditor 4 will automatically get equivalent configuration generated for them, including a similarly configured toolbar. Text formats that were not using CKEditor before (no text editor at all or a non-CKEditor one) will also get an approximate toolbar generated for them, if they have HTML restrictions configured in their filters.