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Dear Sandra Snyder ,
Good day! Thank you for posting to Microsoft Community. We are happy to help you!
According to your description, delegate access can be granted on Outlook for Windows, Outlook for Mac, Outlook on the web, Outlook for iOS, and Outlook for Android. You can find more information about how to delegate permissions to someone else in this official document, please kindly refer to Allow someone else to manage your mail and calendar - Microsoft Support
Please also kindly open your normal mailbox account on the new Outlook for Mac, after that click on Tools menu > select Accounts option > click on first option "Delegation and sharing" > select "Shared with me" tab > click on (+) button and add the shared mailbox account > click on Done.
Note: user has full access permission to add shared mailbox account.
Besides please also kindly refer to this official document to check whether it can help you. For your reference:
Manage another person's mail and calendar items - Microsoft Support
Add and manage delegates in Outlook for Mac - Microsoft Support
Open a shared Mail, Calendar or People folder in Outlook for Mac - Microsoft Support
Options for sharing and delegating folders in Outlook for Mac - Microsoft Support
If you still need other help, please provide me with more details so that I can do more research and testing, thank you.
Thanks in advance for your understanding! Your patience and cooperation will be highly appreciated. Hope you all the best!
Sincerely,
Kerry Chen | Microsoft Community Moderator