http://isdb4l77sjqoy2qq7ipum6x3at6hyn3jmxfx4zdhc72ufbmuq4ilwkqd.onion/docs/guide/secret-groups.html
Link to join group If you are a group owner or admin, you can create a link that can be used by anyone to join the group, making a group more public. Open a group conversation. Tap group name. Tap on "Create group link. Once the link is created, you can also change the role assigned to members when they join.