The current CKEditor 5 build requires the following elements and attributes:

Problem/Motivation

Unable to use the module on a D10.1.x installation.

Steps to reproduce

Try to enable the HTML purifier filter on a text format, e.g. /admin/config/content/formats/manage/full_html
Trying to save, there's the error

The current CKEditor 5 build requires the following elements and attributes:
<br> <p> <h2> <h3> <h4> <h5> <h6> <strong> <em> <code>
The following elements are missing:
<br> <p> <h2> <h3> <h4> <h5> <h6> <strong> <em> <code>

I don't know if this may be relevant: https://www.drupal.org/node/3283526