WordPress 6.6 unified the different slots and extensibility APIs between the post and site editors.

Please check the extension and validate the following along with the version bump issue:

• Check if the plugin is integrating twice, once with wp.editPost and once using wp.editSite
• If yes, then update those to use wp.editor global variable (@wordpress/editor package or wp-editor script handle) as noted here https://make.wordpress.org/core/2024/06/18/editor-unified-extensibility-apis-in-6-6/