Outlook for the Web offers a way to mask the attendee list in a calendar invite. This will prevent someone from seeing who is invited, or if they "Reply All" to a calendar invite, all invitees will not be emailed. It is like BCC but for calendar invites.
Here is how to do it:
- Navigate to Outlook Web Calendar on your browser using https://outlook.office.com/calendar
- Click on New Event

- Click on Response Options, which is the icon to the right of your attendee list.

- Make sure the Hide Attendee List option is enabled as illustrated in this picture:

When you have completed setting up your meeting invite, click Send.