Welcome to the Asana Community Forum @anon93177530.
Currently it is not possible to hide tasks from users.
I’d say yes and no. Let me give you an example:
I am working at an international company and we handle a lot of things for various markets, in various languages. Now the main coordinator and key people involved will have access to the main project to which all tasks are added to, while other people are only added to separate projects. Why? Because they do not need to know about all the other tasks. We are splitting the info up.
A lot of times we also have one main task with subtasks and only subtasks are multi-homed in the relevant 2nd project.
Not sure if you mean “duplicated boards” as duplicated or just multi-homing, because multi-homing tasks is super fast and easy.
Now here is a feedback request thread you might be interested in upvoting as this could be a workaround if you want specific information not to be seen by everybody: Allow Project Owners to Hide & Make Read-Only Custom Fields, The ability to hide Custom Fields applied to a task that don't belong to the project in which the task is being viewed
Oh and also connected work links are very nice: Coming soon! Connected work links! 🔗
Whenever we need to add some confidential info to tasks that should not be seen by everyone we do it via connected work links, meaning we have a task in a private project and add the link to the main task. This way only people with access will be able to see this info.