The 'Assigned to' person in the universal task record is restricted to close the Universal task record. 'Assigned to' write access is restricted through a field level ACl and as per the design if the current logged in user is the 'Assgined to' person then the system not providing the edit access.
Due to this, I'm wondering how the 'Assigned to' person expected to close the universal task by design OOTB.
