AGI Not for sure. Their screenshot is strange. The chose a high voltage divider and the voltage is displayed just above zero, which makes it impossible to analyse small fluctuations. And you can see the line is not perfectly flat. While this is probably not PWM it might be some smaller flicker. It is unclear if small flicker has an effect, too.
The OS eye strain is probably not related to PWM. But to be sure one would need to analyze a device before and after upgrading.