There is no star in Leverkusen. They're mostly just potential players.
Even Florian Writz who is their best player to me is not a star. He may be a star in the team, but he's not a star in world football.
A star player to me is a world class player that has proved himself in over 3 years. Writz can go to another team and not be a star despite how he has been good at Leverkusen.
Xhaka was at Arsenal for a long time but he was never world class, he not still among the top 10 players in his position in the world so how is he a star? There would be teams where he won't be among the first 11.
So it's safe to say there are no proven star players in Leverkusen, even their coach is not a star coach.
Calling a player star is a really big thing. That player needs to carry some specific features to be called that in my opinion. Florian Wirtz is a really promising player but I'm not sure about whether he is a star yet. I would call players like Haaland, Mbappe and so on as stars now. Therefore Wirtz need to go a long way down the road for that.
Before anything else Wirtz needs to be transferred by a much bigger team and show his skills there as well. Then he would definitely be a star in a short time. He is really skillful so I believe in him to adapt to a much bigger team as well.