How do I restrict task access?
If an employee has access to one of a project's tasks, this by no means implies that they will have access to other tasks in the project. Access to each individual task is determined by the rules you set.
Other employees and clients linked to your account will not have access to the task. If you want to link other people to a task, add them as participants or assignees in the Task details panel.
You can see who has access to a task in the Permissions panel: