Microsoft has released an updated version of Outlook for Mac. The new version has many new features as well as some known issues, including a significant issue related to shared mailboxes/resource accounts (see Features & Known limitations). 

Switching to the New Outlook experience:

1. Open Outlook for Mac.
2. Go to the Help menu.
3. Select Try the New Outlook (or toggle the switch if available).

Microsoft provides full instructions here: New Outlook for Mac - Microsoft Learn

Important Changes to Legacy Outlook for Mac:

Microsoft has announced that support for legacy Outlook will end in October 2025 for all Microsoft 365 accounts. For more details: End of support for legacy Outlook for Mac - Microsoft Support 

• Starting mid-August 2025, the option to switch back to legacy Outlook will be removed.
• By mid-October 2025, switching back will be fully disabled for users on the Current Channel.

Features & Known Limitations

Information Services has identified the following issues with new Outlook:

• Delegate rights to the Inbox only for a shared mailbox will not be able to open the Inbox and will need to continue using the Legacy Outlook experience. 
• Full Access will continue to work in the new Outlook experience
• Calendar access will continue to work in the new Outlook experience

Microsoft has a comprehensive list of both the new features and known issues that can be found here: 

• Outlook for Mac - What's New
• Outlook for Mac - Known Issues