TYPO3 Core

As far as I understand it, div-Tags are allowed by default (https://docs.typo3.org/c/typo3/cms-core/main/en-us/Changelog/8.0/Breaking-72837-RTETransformationsAllowDivSectionsByDefaultAndRemoveFont-specificParsing.html#breaking-72837-rte-transformations-allow-div-sections-by-default-and-remove-font-specific-parsing).

My styles.content.allowTags are the default - also containing div

My processing.yaml contains

processing:
  mode: default
  # Tags that are allowed in the content in general
  allowTags: 
    ...
    div

Divs are also allowed in ckeditor by using htmlSupport - { name: 'div', attributes: true, classes: true, styles: true }

The div shows up in ckeditor until I press the save-button. After this, the div is stored in the database but replaced by p in ckeditor and rendered as p in FE.