Click Calendar Icon in lower left corner In the left side bar Right Click the calendar you want to share, then click Properties. Click the Permissions tab Click Add to add permissions for a new user, or click the name of the existing user in the list to change their current permissions. You can grant access to your Calendar, Contacts, Inbox, and any other folder or subfolder. If you wish to update permissions to a higher level, highlight the folder. PC users must grant 'full details' to the Outlook Mac user.

Honestly, if the Out of Office options are greyed out, it sounds like the account was not added as an Exchange type account (IMAP instead).

All prices on this site arefor Electronic Delivery. Aatrix micr font. Please add it to your grand total.

What is the server, in-house ? If so, what version and SP level of Exchange ? Needs to be Exchange Server 2010 Service Pack 2 or later, per https://support.office.com/en-us/article/General-requirements-for-Outlook-2016-for-Mac-A07A593D-B383..

I have an account with MS-hosted Exchange (not Office 365 but the completely equivalent Exchange-only MS hosting) and this 'just works,'

both adding a shared calendar and Out of Office settings.

For the desired calendar, ask your Exchange admin to verify permissions settings/access for this user.