"Invalid object name" error when executing query
I'd guess the problem is your SQL Server login does not have it's "default database" properly set.

This will show you what your "default database" is set to:

SELECT sp.name
    , sp.default_database_name
FROM sys.server_principals sp
WHERE sp.name = SUSER_SNAME();


You can either change the default database of your login, or you can specify the database in the connection string.

This will modify your default database:

ALTER LOGIN &lt;login_name&gt; WITH DEFAULT_DATABASE = [testDB];


If you want to specify the database in the connection string, make your connection string:

SqlConnection con = new SqlConnection("Data Source=ANUPAM-DESKTOP\\ANUPAM;Integrated Security=True;Connect Timeout=30;Encrypt=False;TrustServerCertificate=True;ApplicationIntent=ReadWrite;MultiSubnetFailover=False;Initial Catalog=testDB");