Mirror Create Player From Client and Change Scene

I’m very new to Mirror in Unity but I have a lot of experience in Network-programing.

I’m currently trying to create a Game, where the Player’s data is stored on the client, and can join different games (not concurrent) with his/her character. (Likely to Terraria)

So I can’t use the automatic Player creation of the default NetworkManager class. After clicking "Join/Host" in our Main-Menu I want to change to the scene the player has played in, Hosting/joining a server and create the player on the server with the specific position…

I have tried now multiple attempts to do this, but none of mine seemed to work. Am I the even possible to have the players in different scenes with ease? Where/When should I create the Player so isn’t null on the Server?