As you know, when you are using Exchange Online (and as such Exchange Online Protection) for inbound mail traffic, you receive a quarantine notification when some emails have been put in quarantine.

Well, this notification will also be sent to shared mailboxes too.

The rolling out is planned for mid-May 2020.

This update will allow any users having access to the shared mailbox to use the quarantine notification email to check/release email instead of having to logon to the website.