this is a simple solution for those, who needs more outputs or inputs for your GX device:
There is a cheap (less then $10) network module available on AliExpress or Ebay called "Web_Relay_Con V2.0 HW-584". It has 16 I/O ports.
It doesn't work at all out of the box, as the firmware is really bad. But Michael Nielson is doing great work and made this little board working and, among other things, MQTT capable. His FW and more info is here: https://github.com/nielsonm236/NetMod-ServerApp
I've tried it with Cerbo GX, Venus OS Large and Node-RED and works great. I'm using it to control these relay boards with optocouplers. Refer to Michael's manual, not all relay boards are compatible.