Tiny green dots all over my screen in games

And the flip side: if the dots DO show up in screenshots, it's the gpu, not the cable. Undo any overclock first, especially a memory one, then check the card isn't running hot. Memory artifacts often look exactly like that, green or purple specks.

The fact they don't show in screenshots is your best clue. A screenshot grabs what the graphics card rendered, so if the dots aren't in it, the frame was fine and something goes wrong after it leaves the GPU, cable, port or the monitor itself. Sparkly specks in dark scenes are a classic flaky cable symptom, especially displayport. Swap the cable first, then try another port, then drop the refresh rate a step and see if they vanish. If they follow the monitor onto a different PC or console, it's the panel.