I don’t know if it’s in clear text or not. But I’m not sure why you’d be worried about changing your WiFi password. The person you sold it to would have to come within a couple of hundred feet of your house and… Then what? Use your router to download porn? It seems unlikely. Your only exposure would be if you had wide open file shares on your PCs…and again, what would impel the buyer to go to all that trouble?
I doubt Wyze keeps any Wyze credentials on the camera, so you probably didn’t need to change that either. Just delete it from your account.