MacBook Air 2012 Lagging (e.g: cursor not smooth)

Hi,

I've just installed Catalina on my MacBook Air 2012, but everything just not smooth right after OS installed! Like, cursor lagging, video choppy, even loading slow while surfing a website/each page.

Therefore, I tried to reverted the OS - Mojave to check whether it'll solve the issue?! Unfortunately, no luck at all, same issues occured!

What's wrong?

PRAM, SMC RESET, SAFE MODE ... All those standard solutions already tried!

Some said caused by CPU Overload... Overheating...

What should I do?