Hi TJ,

This option is available when Domain Admins view a subscriber. Log in as the Domain Admin, edit a mailing list, click on the Subscribers tab, then click on the subscriber's email address. In the Subscriber modal that opens up, click on the Subscriptions tab. This will show a list of all mailing lists, allowing you to easily add or remove the subscriber from multiple lists at a time.

Keep in mind: Just like in version 15.x, this option is only visible to Domain Administrators. If you've made an end user a moderator of a mailing list, they will not see the Subscriptions tab when editing a subscriber.