If you installed SQL LocalDB along with SambaPOS then there really isn’t any need for SQL Auth because it is a single-user Engine… and I’m not sure, but it wouldn’t surprise me if SQL Auth does not even exist in LocalDB… it probably only uses Windows Authentication…
You can still use SSMS to login to LocalDB and check things out.
One way to tell if you are running LocalDB or Express is to look at Windows Services. Express runs as a Service (listed as SQL Server (InstanceName)), while LocalDB does not. LocalDB does not appear in Windows Services since it runs as a task that you can see only in Windows Task Manager.
I don’t know for sure, but since LocalDB supports only single connection/user it might also support only a single Database, which could partly explain why the method described above does not work for you.