PWM (Pulse Width Modulation) is something that all of the OLED iPhone models suffer from, which includes my current iPhone 13 Mini. This post gives a good overview of how you can help reduce this if you notice it.
I made a quick video showing what this looks like on the iPhone 13 Mini in real life.
This was to help anyone that does experience eye strain or worse due to this approach to screen dimming and want to get an iPhone 13 Mini. I hope this helps you make your decision before buying then needing to return.