If your eyes are sensitive to flickering displays, then it may be best to avoid Samsung's latest flagship. The Galaxy Note 9 display flickers at a frequency of 227 Hz that could potentially cause headaches and tiredness. The practice, known as pulse-width modulation, is rarely seen on smartphones.
https://www.notebookcheck.net/Take-caution-Samsung-Galaxy-Note-9-display-flickers-by-design-and-could-cause-eyestrain.325712.0.html
To my knowledge, no OLED display hasn't got PWM, so not really a surprise here.
Almost everything that uses a display will use some sort of PWM. It is a very common practice that reduces battery usage as it is more efficient to turn the display on and off very fast rather than to just leave it on
Instead of PWM some manufacturers use P-OLED display with voltage control (LG G Flex 2) or hybrid approach (PWM + voltage control) (Nexus 6, Moto Z2, iPhone X)
The final message is: go in a shop, and try it. Maybe you'll feel it, or maybe not. But try it before you buy it !!
I wonder what determines the frequency of the PWM.
Here's a list of devices with their PWM: https://www.notebookcheck.net/PWM-Ranking-Notebooks-Smartphones-and-Tablets-with-PWM.163979.0.html
Spoiler: the iPhone X, S9, S9 plus and other OLED display phones have similar PWM.
Glad that notebookcheck reports this stuff.