Shared Calendar improvements are now enabled by default in the most recent versions of Outlook, in all update channels for Microsoft 365 Apps. The Semi-Annual Enterprise Channel was the final update channel to enable the Shared calendar improvements by default (in version 2202, released on July 12, 2022).
Additional information on what calendar sharing updates are: https://support.microsoft.com/en-us/office/calendar-sharing-in-microsoft-365-b576ecc3-0945-4d75-85f1-5efafb8a37b4
Enable or disable the Outlook calendar sharing updates:
1. In Outlook, select File >Account Settings >Account Settings. You will see a list of your email accounts.
2. Select your Microsoft Exchange account.
3. Choose More Settings, followed by the Advanced tab.
4. Select the checkbox next to: Turn on shared calendar improvements. (You can turn on/off the shared calendar improvements with this checkbox.)
5. Close and restart Outlook.
Opting into these improvements do not impact your experience with your own calendars and you can go back at any time.