In 16.x, notification profiles were removed, so the event action "Use Default Notification Profile for User" is no longer available. However, the ability to send users a personal disk space notice is still available in 16 and 17.
When creating a system level disk space event, you'll find an action for "Send an email and notify the user". This will email the user, send them a browser notification, and add an entry in their Notifications window. If you'd like to be notified as well, add a second action of "Send an email" with your address in the To field.
This functionality is also available in domain events, but you'll manage it a little differently. In the "Send an email" action, it should be possible to use variables - either #emailadress# or #username#@#domain#.
However, in my testing, I've found that there may be a bug related to the user disk space event or variables in the email actions. I've reported my findings to the development team so they can fix things and ensure this functionality is available.