Microsoft has announced that the switchover to the new OWA interface will start on July 22 when Office 365 tenants in targeted release will lose the chance to toggle back and forth between the two interfaces. By the end of September, everyone will use the new OWA. Let’s hope that Microsoft has fixed all the functionality gaps by then.
https://office365itpros.com/2019/07/05/new-owa-becomes-the-owa-july-22/
