mqttnet.cs

var options = new MqttClientOptionsBuilder()
    .WithWebSocketServer("some ws server")
    .WithTls(new MqttClientOptionsBuilderTlsParameters { UseTls = true, SslProtocol = SslProtocols.Tls12 })
    .WithCredentials("some credential", "some credential")
    .WithClientId("some clientid")
    .WithCleanSession()
    .WithTimeout(TimeSpan.FromSeconds(100))
    .Build();

try
{
    await mqttClient.ConnectAsync(options, CancellationToken.None);
}
catch (Exception ex)
{
    _logger.LogError(ex, "Connecting to MQTT WebSocket Server failed");
}

_logger.LogInformation("MQTT Connected: " + mqttClient.IsConnected);
return mqttClient.IsConnected;