Staff members can add notes to a patron via "Add message" button in patron details. This can either be an internal message for staff only, or it can also be visible to the patron in OPAC. When visible in OPAC, it would be useful to also notify patrons of the new note through other communication methods, like email or sms.
I propose adding a new message attribute such as OPAC_Message, making this type of message configurable in patron messaging preferences. The form itself would get a new dropdown menu "Send notification" with the following options - Do not send (default) - Notify of a new OPAC message (this would inform patron there is a new message and a link to OPAC to see it, GDPR friendly) - Send message content (this would send the message content as is) Default option could be configurable through a system preference.