Ok, so at first i thought it only happened when watching youtube videos, but everything else is also being rather stuttering/choppy... How do i fix this? I just added a 1440p screen to my pc... it's my only 1440p screen, so can that be the reason for it, or? Here's a video how it looks like:
What is your GPU ? Maybe it might be throttling because of the display itself. Try installing new graphic drivers and if it didn't fix the issue , I suggest to adjust your PC resolution to a lower scale.