We have implemented a SharePoint Framework webpart called "Sending Messages to multiple teams" like broadcasting to specific teams using Graph API. We came up with this by observing the MS TEAMS functionalities, As forwarding  messages option is not available in Desktop as well as in Web client. So in our webpart we included a  TextField where we can enter the messages and /or upload a file control and list of joined teams of members. After clicking on send button messages will be sent to selected teams. We have implemented using SharePoint Framework, TypeScript