without using your package directly,
I installed Laraveli, then I installed the necessary packages vue, vuex etc. everything is same as your package,
then I installed "https://laravel.com/docs/8.x/sanctum" then I copied and pasted the same controller as yours, everything is ok, there is no problem when signing up, but 401 "{message: "Unauthenticated."}
I get message: "Unauthenticated."" error.
this is a vague issue , you are using only the auth classes as i understood . which makes it difficult to debug ,
but my guess this could be a related issue issue
without using your package directly, I installed Laraveli, then I installed the necessary packages vue, vuex etc. everything is same as your package, then I installed "https://laravel.com/docs/8.x/sanctum" then I copied and pasted the same controller as yours, everything is ok, there is no problem when signing up, but 401 "{message: "Unauthenticated."} I get message: "Unauthenticated."" error.