Hi @CharlieLor ,
so that option I'm looking for is NOT available in the Mac version then, correct?
Yes. It's currently not available in Outlook for Mac. Below is a similar feature request posted in the official feedback portal for Outlook. Let's add votes there and hopefully this can be realized in the future.
https://feedbackportal.microsoft.com/feedback/idea/46d66991-b995-ec11-a81c-000d3a0f04fc
By the way, if Patchfox's reply has been helpful, please consider accepting his post as answer by clicking the "Accept Answer" button. This can help increase visibility of this question for other members of the Microsoft Q&A community. Thanks!