To get started, you can always open and that’ll work.
Assuming you haven’t left Hangouts for another messaging service from another provider, switching to Chat is probably a good idea at this point. Today, basically as a part of a big Google Workspace announcement and after a bit of a preview period, Google Chat is available to all if you are interested. This slow death of Hangouts has given people all the time in the world to transition over and get on Google Chat, the company’s modern messaging app. The end of Hangouts will probably happen without anyone really noticing because Google has made its replacement readily available.