Directus FLows: Item.create and Item.update have different data structure about directus

[br41nslug]

however when making an update to an existing entry, the id is not written in the form of the attribute "key" but the array with one element.

This is intentional since you can also update multiple items in a single update. https://docs.directus.io/reference/items.html#update-multiple-items

The insonsistency is also that the whole actual entry attributes are ommited and: only the fields that were updates are passed which creates further inconsistencies.

That is consistent with the update action done, updates can be partial (for example a single field) where creating an item will always at least have the required fields. If you want the full entry you will need to fetch that from the database in an update event.

This leads to an error where once I'm updating the data I am unable to set the correct ID as it's returned in different formats.

This is something you will need to check for in your flow/extension. I would personally recommend creating 2 flows one for creation and one for updating (and perhaps a third for delete events as that structure differs too)