I selected a task of his and clicked on Unfollow (I am the administrator for this company)
I thought by doing this it wouldn’t give me updates on this task
but instead it’s removed that sub task from my view so that I can’t see it anymore.
Do you have access to the project or parent task by any chance? If you do, you should be able to access the list of subtasks and follow the one you’re missing.
Alternatively, if you know anyone else following this subtask, they should be able to add you back as a collaborator.