When you open your Calendar in Microsoft Outlook for Mac, the "Open Shared Calendar" button on the ribbon is unavailable (greyed out).

Your TechMail account may have been added to Outlook as a Microsoft account instead of a TTU Microsoft 365 account.

1) Open Outlook for Mac.

2) On your Mac's menu bar, click Outlook and then Preferences.

3) Click Accounts.

4) In the left-hand pane, click your TechMail account.

5) On the right side, look above the field labeled "Account description". If the type of account reads "Microsoft Account", remove your TechMail account from Outlook.

6) Add your TechMail account to Outlook. (On Step 8, look above "Account description" and verify that the account type is "Exchange/Office 365 Account".)

Outcome

You will be able to use the "Open Shared Calendar" button.