Hi @HILLIARD, Emma
Welcome to our forum!
Based on my research, New Outlook cannot add a shared inbox to favorites at present. It is by design, i am afraid you need to turn back to the legacy Outlook to use the feature.
Please kindly understand that many functions are not designed at present. To get this feature more quickly, I have found a post in feedback collection website, and you could vote for it. Many features of our current products are designed and upgraded based on customers’ feedback. You can also make suggestions on that website and hope Microsoft will notice this in the future.
Thanks for your understanding and support!
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