Photorealism is a drawing tool. An account is entirely optional and only exists so your references can appear on more than one device. You can delete it at any time, and you do not need to contact anyone to do it.
This is immediate and permanent.
Everything the account holds: every reference image uploaded from it, every photograph of your drawings that was synced, every record of their names, dates and settings, and the login itself. None of it is recoverable afterwards, and no backup copy is kept.
The copies already on your phone or tablet are yours and are left alone. Deleting the account removes what is stored online, not your work. If you want the local copies gone too, delete the individual references in the app, or uninstall it.
If you have lost access to the device, ask through the Photorealism Discord, linked at the bottom of the app's project page, from the email address the account uses. Requests are handled within 30 days.
None. Photorealism keeps no copy of a deleted account or its files. Anonymous usage counts, such as "the app was opened", contain no account information and cannot be traced back to anyone, so there is nothing in them to delete.
See also the privacy policy. This page covers the Photorealism web app and the Photorealism apps for Android and iOS.