I found a portable OLED reading light but didn't find reviews so I picked it up and measured the flicker. Product name is "OLED RL101". The device has an integrated battery that can be charged via USB.
After you switch it on, it runs at full brightness. No flicker at full brightness:
But as soon as you start to dim the lamp, there's 100% (full on/off) 260 Hz flicker:
Additionally, there's flicker for about 0.7 seconds while turning the device on and off. Because they decided to show you a fading light and used PWM for that.
I will see if the lamp is usable for me at full brightness and how long it lasts (probably not long). The flicker range is definitely not usable.