Hi!

I use a class like the following for connection to the database. If you want you can add the certificate to your application. Otherwise you must set the Field TrustServerSideCertificate to true

public class DatabaseSettings
    {
        public string Hostname { get; set; }
        public string Username { get; set; }
        public string Password { get; set; }
        public string Name { get; set; }
        public bool DisableSSL { get; set; }
        public int Port { get; set; } = 5432;
        public bool TrustServerCertificate { get; set; } = false;

        public string GetConnectionString()
        {
            var applicationName = Assembly.GetEntryAssembly().FullName;

            var connectionBuilder = new NpgsqlConnectionStringBuilder
            {
                Host = Hostname,
                Database = Name,
                Username = Username,
                Password = Password,
                Port = Port,
                MaxPoolSize = 50,
                ApplicationName = applicationName,
                TrustServerCertificate = TrustServerCertificate,
                SslMode = DisableSSL ? SslMode.Disable : SslMode.Require,
            };

            return connectionBuilder.ConnectionString;
        }
    }