Create a shared calendar in M365

1. In Outlook, select the calendar icon.
2. On the Home tab, choose Add Calendar, then From Address Book.
3. Add users to the shared calendar by entering their name or selecting their name from the list, and then choose OK.
4. You can now view your calendar and the calendars for the people you added.
5. To check your group's availability, choose the Day view.

https://docs.microsoft.com/en-us/microsoft-365/business-video/shared-calendar?view=o365-worldwide