That's true, but might not be too hard to reverse engineer. If all we need is a trigger for the ATU, I think that's very easy to find.

Sure - happy to share it.

On software side I just use example ptoject from IW7DMH esp32 TCI library with those one minute done modifications:
1. defined GPIO pin for ATU triggering output, initialize GPIO and for sure hold it down - modify file TciDemo as shown below, lines with yellow marker:



2. In Events file just modify event handler for Tune this way (yellow marker):



You have to connect to ESP32 devkit by serial console at 115200 Bd, type help and follow setup (wlan ssid, wlan passwd, host IP, port..) Set parameters are stored in NVRAM, no necessary to set it up again. Then It should work, don´t forget to set Tune power somewhere between 5 to 10 W.