XTU only supports X and K processors. You have a G processor. Your processor is not supported.
On the XTU download page, it tells you what processors are supported. It also says " Intel XTU may or may not work on unsupported processors."
Also, regarding undervolting"
I'm sorry but this is not true. The i7-8705g has a partially unlocked multiplier, and as I said in my post, I was previously able to overclock (up to 4.5 GHz) and was doing so for several years (I rarely went that high, but nonetheless it was an option).
And, Dude, as I have shown you in the documentation, it says " Intel XTU may or may not work on unsupported processors.".
This is a case of NOT. And, nothing is forever.
Good luck moving forward.
My understanding is that, in response to Plundervolt, Intel has made changes to the microcode that alters or removes the capabilities for undervolting. You are not the only person who has lost a capability here, but Intel had no choice; vulnerabilities must be addressed.
Thus does Doc's "nothing is forever" get applied, unfortunately.