Using older versions of Outlook for Mac for personal email and calendar
Great, this seems to work on my Mac as well. I just reversed the process: I switched from "new" to "old" composed a message there with an emoji, and then back from "old" to "new". Now it works, also after a restart.
A simple solution to an issue that drove me nuts for months. Glad I found this thread. Hopefully this issue is now gone forever.