It's a mobile CPU 7040 series and you can't undervolt it. But you can limit TDP using a tool like ryzenadj.

I set it to 20W on battery and the full 51W (or what it was) while connected to AC.

Not sure about lottery because this is my only Ryzen PC, I think a 7840U might run a little lower though, if I'm not mistaken about the binning process.

Take note this is a real idling wattage when it's not doing much at all. At the time when I tested this yesterday, I only had a terminal and browser open (Linux), and turned the screen off via dpms.

https://postimg.cc/XGb3sV0F (0.87Wh in 20m20s ~2.56W/h)

With wifi off it approaches 2W