Google is updating Hangouts to Hangouts Chat as of May 20, 2019.
To use the new Hangouts Chat, simply open a new tab in your browser and go to chat.google.com. Or if you prefer a standalone app, you can download it here - https://chat.google.com/download/
Any group messages you may have created in Hangouts will no longer be visible in Hangouts Chat, but new groups can easily be recreated as rooms. For more information about using Hangouts Chat, visit this G Suite Learning Center webpage.