pocketmine\level\Level::getPlayers PHP Method

    public function getPlayers() : array
    {
        return $this->players;
    }

 public function despawnFromAll(Level $level = null)
 {
     foreach ($level instanceof Level ? $level->getPlayers() : Server::getInstance()->getOnlinePlayers() as $player) {
         $this->despawnFrom($player);
     }
 }