Take a look at the Spaces list to see the icon next to the new spaces. After you open the space for the first time, the icon goes away.
If you leave a space and get added to it again later, you'll see the icon again.
You'll see the icon on Webex Teams for iPhone, iPad, and Android, too.
Webex Teams | See When You've Been Added to a New Space
You can easily see when you've been added to a new space in Webex Teams. You'll see an icon next to the space or team space name on the spaces list.