Check the full post for a Teams feature update. If you're using macOS and want to explore the latest features, try Teams via Firefox; the macOS native Teams app hadn't been updated as I typed this (the Windows native app had been updated) [update ~12 hours later: new macOS Teams app has been released], and Safari isn't supported (it reports "Microsoft Teams will be available on Safari very soon! In the meantime, try out our desktop app."); Teams in macOS Chrome advises "D'oh! To open the web app, you need to change your browser settings to allow third-party cookies."
"New features in Microsoft Teams make it an even more powerful hub for teamwork by enabling you to use apps in new ways—including the ability to command apps and take quick actions from the command box, as well as include content from an app in a conversation. This marks the biggest single release of new functionality since Teams launched last March."New ways to use apps and get more done in Microsoft Teams - Office Blogs