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).
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.
Apr 28 2021 02:13 AM. Re: Send Button Greyed Out For New Messages. It was greyed out after i clicked 'invite' and added new email addresses. Workaround: Before i clicked invite, the 'send' button location was 'save and close'. I saved and close first. Then opened that meeting and clicked 'invite'. Now i can click send. I've also tried a different account but that is the same (ie greyed out send button). Exporting reports requires Microsoft Excel 2016, 2013, or 2010 or Office 365 (includes 64-bit) I try to add a new email account to Outlook 2011 for Mac. The button exists of course, but is greyed out and not clickable. That DefaultIMAPP is set to “Lync”.
For the desired calendar, ask your Exchange admin to verify permissions settings/access for this user.