Nintendo ends support of Google & Apple logins early 2027 so you need to create Nintendo Account

Nintendo has confirmed via its Japanese support site that those of you who have chosen to log in with Google or Apple accounts will need to set up and use a Nintendo Account. The service for logging in with a Google or an Apple account will end on 26th January, 2027 so you will certainly want to have created a Nintendo Account beforehand.

“After the service ends, you will no longer be able to log in using your Google or Apple account information. For devices that are already logged in, you may be able to use them without logging in again. However, if a login screen appears, please log in using your Nintendo Account email address (or login ID) and password or use your passkey.”