Mouse pointer stuck and high cpu load, new system. Why?

Hello everybody,
I'm writing here 'cause I'm almost desperate...
My friend's pc "AllInOne" Asus ET2020AUKK in practically unusable: in every situation (also just after the boot), also just moving the mouse, the pointer is not moving smoothly but it gets stuck and then suddenly jumps a part of the screen... It has been like this since long time, and the problem has not been solved even with the last updates. I've execute scans for virus or malware, but without success.
I was thinking it was caused by the original old HD: now I have replaced it with a SSD and I have done a clean installation of Win10 1909, with all the suggested updates. I've not installed anything, the system is still "vanilla", but the problem is still there!!!

If I look at the system monitor I see that the CPU load is always too high: with only the system monitor active it is about 15%, with momentary peaks at 50%. The process at the top of the list is "System". The graphic shape of the load is like a "saw tooth", with the various peaks at at the value of about 15% and spaced about 1.5/2 seconds.

The weird (for me...) thing is that if I start the system in "Safe mode", the problem disappear and all is very smooth.

I've also tried to disable some hardware in the bios (ethernet, wireless and sound cards), but without success.

Has anyone any idea about what is the problem, or at least what can I do to find the cause?

Thank you everyone in advance,
bye!
B.

- - - Updated - - -

Up! (please...)

Bingo!
Thank you so much Caledon Ken, you have correctly identified the cause of the problem.
The windows 10 driver for the vga card does not work in my pc, neither the original amd driver. I have to install the vga driver released directly by Asus, the manufacturer of the pc.
But Asus does not have released a version for Win10, only Win8.1. But anyway it works. I have to inhibit windows update to update this driver, and I have done that with the Microsoft tool wushowhide.cab http://download.microsoft.com/downlo...owhide.diagcab

Again, thank you so much! You have solved a problem that haunted me since long time!

Bye,
Brune.