As we announced at Microsoft Ignite 2019 this morning, we are excited to confirm that Multi-window capabilities are coming to Microsoft Teams, and will start rolling out to the public ring early next year!
Alex & the Teams teamJason Davis commented
Chat should be able to stand alone and independent of the Teams section. If I am presenting in a Teams meeting I need to be able to chat with members on a second screen. Teams does not allow this functionality which greatly hinders communication.