Everything you have kept, in the two places it can be kept — this browser, and your account. They are separate on purpose, and the page says which is which.
Nothing on this site needs one. Every tool works signed out, unlimited, and what you keep goes into this browser and no further.
An account does two things and no more. It raises the reading limit from three a day to fifty, because a name attached to the cost is a cost the site can carry. And it keeps your readings server-side, so the one you asked on your phone is there on your laptop.
We store the question you asked, what was drawn, the reading, and the source text it was written from. That is the whole list, and you can delete any of it here, permanently, without asking us.
Saved server-side because you were signed in when you asked. These follow you between devices. Deleting one here deletes the row itself — it is not hidden and it is not archived.
The notebook. It lives in this browser, has no account behind it and no copy on any server. Clearing your browser data clears it, and another device has never heard of it. This is what the Keep button on every tool writes to.