As far as I can tell, its header is like the status of a main account:
– you have logged in, indicating "username" with a balance and "Upload" CTA
– guest, indicating "guest" without additional information
Now, the registration process is related to the account.
If users can play without registering, there should be a separate CTA to create an account (it's a separate process from the game itself). That CTA should be in the header.
On the other hand, if your game requires new players to create an account, then be sure to go ahead and offer them an account creation screen after clicking on the main CTA (if possible within the application so that users do not have to leave) return later).
In that case, you do not need a CTA in the header to create a new account, simply "Load" the CTA for existing users.
But if your application allows players to continue playing as guests, after clicking on the CTA main menu, it offers a screen where they have 2 options: "Continue as a guest" or "Create a new account".
In that case, there is still an optional CTA in the header for new users to create an account, and playing a new game simply reminds them that there is an option (and a possible benefit) to create a new account.
That way, they do not feel forced and can choose their own time to make an account.