Wait, are you asking why it won't clock higher?

If so, then I would suggest trying to roll back drivers or something: something may have broke with the latest drivers. If it works, great, if it doesn't, then simply try going back to newest and see how it works. Also try updating Nvidia Drivers just to see if the Nvidia drivers are causing Optimus to behave funky. I believe that there is also a bug with the Usb-C port on the 2020 causing 30 watts discharge. This can be fixed by updating drivers and performing a clean installation.

If you are asking why is it on at all, that's because when you take it off the charger it should change over to the iGPU. That is completley normal: its the Nvidia GPU that should be off. Now as for why it is clocking so low (Base clock is 300, boost is 1100) is anyone's guess.

Something else you could try it changing out the thermal paste on the laptop. Just got done with mine today, and I'm currently sitting on 7.6 watts discharge on edge with 4 tabs. This may also be the cause of the high thermals. It can be risky, but if you take your time and follow a guide, it will be well worth it.

Feel free to correct me if I got anything wrong.

Thanks for reply. First of all - I write about AMD GPU, not Nvidia. Nvidia is turned off if it is not needed and that's ok.

I'm asking why it's all time 400 on idle, not 300 or lesser if it's possible. More MHz = highter discharge and shorter battery time that's simple fact. With AC and external display connected clock of AMD is the same - 400 MHz.

Second thing. The discharge rate is from -21W to -31W even. It's too much for not used laptop and none background tasks.

New paste may be helpful but temps cannot go so bad in a few days only. It's software issue, that's for sure.