That's not good.
https://forums.tomshardware.com/threads/motherboard-cpu-compatibility.2844622/ covers the CPU compatibility angle.
So with all you wrote.
1. 100+C is far too hot. Fix that.
2. I read NOTHING about your OS install. Windows does NOT take kindly to CPU and motherboard swaps. After you fix your way too hot CPU issues, then google about CPU changes and what to do with Windows.
My mainboard is h61m-P20/W8
Bios is 3.6, smbios is 2.7, there is no newer bios on manufacturer website.
The power source is forton 350w, and i tested new cpu without gpu (old cpu works well with gpu turned on, so it can't be a power issue).
I recently updated my g2020 to i5-3570 (second hand, but the seller got very good opinions so i doubt it can be damaged) and the new processor is EXTREMELY slow. I barely can use web browser, games i played on g2020 comfortably won't even turn on.
https://imgur.com/a/ysbxKUo - hwinfo screenshot
https://imgur.com/a/mmHWLqP - temperatures.
As you can see, 2 of 4 cores are not even turned on.
Why is this happening? How to fix it?