There is currently no way to add a person as a true Bcc recipient to a meeting request. If this is a feature you'd like to see in future versions, please provide feedback directly from Outlook by selecting Help > Feedback.
If you want to keep attendees from seeing who else is invited, you can hide the attendee list in new Outlook for Windows and Outlook on the web. When you create or edit a meeting, select Response options > Hide attendee list. Each attendee then sees only the organizer and themselves. This option isn't available in classic Outlook for Windows. For more information, see Attendees can see others' responses to a meeting invitation.