Same as mine..
I open gpu-z and on the sensors tab found somthing abnormal.. the MEMORY CLOCK STUCK AT MAXIMUM... (1750mhz).. EVEN ITS ON IDLE...
I found that the problem is on the Radeon software (adrenaline win 10 / 64bit - Sept 2020 ) ..
I ONLY plug 1 monitor ( on HDMI port with hdmi to vga...