Microsoft announced the preview of the Send from Email Aliases feature on January 25. The only problem is that the same feature was released in April 2021. And OWA gained full support for it in October 2021. So why would Microsoft reissue an existing feature? They're not saying, but I suspect it's down to fixing some issues in the Exchange Online transport service to make sure that messages sent from an email alias work properly in every circumstance.
https://office365itpros.com/2022/01/27/send-from-emaiil-alias/
