Hello Eric,
Good day! Thank you for posting to Microsoft Community.
I understand that your customer is experiencing an issue with shared calendars not being visible when switching to the new Outlook. May I please know whether you have tried to add these calendars in the New outlook? Please see below.
- In the New Outlook, select Calendar
> Add calendar > Add from directory. - Select the account you want to search from. (Your main account in this case)
- In the next field "Select a person...."Type the name of the person, group, or calendar resource and click to input their address.
- Select the group where you want to view this calendar.
- Select Add.
- You should be able to see the calendar.
.
Looking forward to your response.
Best Regards,
Ashraf.