I just bought a new AW15 R4 with the i7-8750H processor. It hit 100*C max temp right out of the box so I wanted to try undervolting CPU (first time messing about with settings).
A bunch of Youtubers were recommending intel XTU but I had issues undervolting with XTU and the changes I made were reset each time the computer rebooted so I opted for ThrottleStop instead.
All problems solved using ThrottleStop. Give ThrottleStop a try if you are having issues with XTU. Seems to be much better. Make sure you follow a good video guide when making changes!
I was able to get my max temps down from 100*C to about 83*C!!!!!