I also have this problem with my ROG Zephyrus M16. I also get much lower performance than I expect. I found that this was worse when the laptop lid was closed (which it often is because I use a docking station and external monitor), so I leave it open now. I feel like this is a problem with the thermal dissipation of my laptop and I am planning or reapplying thermal paste soon if I can manage it. Using the ROG "Armoury Crate" software to turn on "Turbo" mode for the fans helps some too, but its really loud. I'll try to update after a thermal paste reapplication to see if this permanently solves the issue, but using a laptop stand with a fan might be the best option for now.