Missing CKEditor & config button
There appears to be a recent bug, possibly introduced in 5.8 though I'm not certain, that affects the CKEditor, namely missing Configure CKEditor button and CKEditor itself won't appear. See this issue: https://lab.civicrm.org/dev/core/issues/594#note_11806

If you are comfortable working in the database directly you can work around this by deleting the existing setting for WYSIWYG editor and then avoid saving Display Preferences until this is resolved.

DELETE FROM civicrm_setting WHERE name = 'editor_id';



This bug is now resolved in CiviCRM 5.9. After installing the 5.9 update save the Display Preferences &amp; CKEditor settings as per the post-install notice.