Hi Larry.
 
First of all, thank you so much for supporting our work.
 
“Learn ESP32 with Arduino IDE” has a Module that covers MQTT.
 
The “Home Automation using ESP8266” eBook also has some units about MQTT.
 
The “Build a Home Automation System” eBook is dedicated to Home Automation using Node-RED and ESP8266 with MQTT. But the eBook is a bit outdated, in fact, we’ll no longer update that eBook. We’re working on a new eBook that covers Node-RED and MQTT and will replace that one. However, many of the projects still work, but some menus and options are outdated.
 
Regards,
Sara
 

Let me know when the new book comes out. I thank you.
Larry

We will.
It will be available in September or October.
Regards,
Sara