You can better address who can delete or create entities in the access rules tab of the entity itself.
Go to your domain model, open an entity, and go to the access rules tab.
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Furthermore, to check whether someone is the ‘owner’ through the relationship between task_useraccount, you need to go one relationship further (to the administration.account). There you can check if that relationship = [%CurrentUser%]
Example: $currenctObject/Task_UserAccount/(=> refer further to Administration.Account) = '[%CurrentUser%']