Players are allowed to turn off/on the winner broadcast. There is a [ Settings ] button at the right corner on the top bar, in the settings page, there is a [ Announcement] button, you can turn it off/on by clicking the button.

Please notice that if there are still winner broadcasts when you turn off the broadcast, it's normal. The broadcast will continue for a while after you turn it off, but it will stop in several minutes.
(Announcement in off-mode)