When a subscriber does opt out on a newsletter category it would be usefull to add add log activity wich content could be :

• User identity
• Date and time (in GMT) of unsubscription
• Removal method (e.g., link in email, manual action, etc.)

This could be usefull for customer in case of RGPD conformity control on subscribers management

Make this information easy to be get from (CMS and/or CMS Admin)