OP hasn't said anything about the cause of the manager transition. For all we know, it could be just that their old manager left for a better opportunity, and they back-filled the role.
My advice - help the manager as much as possible while you evaluate them. It'll probably be fine, and you'll learn to work with them -- they may even make the team better. If not, start looking.
Imagine you are big name act like Taylor Swift. You would not let some outside rando choose a manager for you, would you? When a manager chooses a manager for you they don't do it for your benefit.