Hi @Brian Hart ,
According to your description, I understand that you would like to add a caledar in your Favorite line, is it right?
If so, please kindly understand that we could only add a folder such as Inbox or draft to favorite in Mail view, and the calendar could only display in Calendar view, so there may be no option to add a calendar to Favorite and display in Mail view(whatever it's your calendar or a shared calendar).
Actually, based on my test, the shared calendars would display under your calendar in Calendar view, and we could open multiple calendar at same time and manage which calendar would display via check or uncheck it like below.
Also, we could view multiple events from different caledars in a calendar via view in overlay mode. Hope these options could also help you manage the shared calendars in your Outlook.
If that's inavalid, I have also tried to find any solution about the related operation or workaround for your requirement, but in vain. If it is inconvenient for you and you really want such feature, it's suggested to vote this similar idea in our uservoice for Outlook, which is the official platform that Microsoft collect the suggestions on Outlook, it may increase the priority for our engineers to create a possible option or feature that can be included in the future updates of the program.
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