iPhone 11 is the last iPhone that uses a Liquid Retina LCD display. All later upgrades make use of OLED panels.

OLED screens (like those in the iPhone 12, 13, 14, etc.) control brightness by rapidly flickering the pixels on and off, that’s PWM (Pulse width modulation).

Even if your eyes can’t see the flicker, your brain and nervous system can feel it.

The iPhone 11 LCD panel doesn’t rely on PWM at normal brightness levels. It adjusts brightness with DC dimming, meaning the backlight intensity actually changes rather than flickering on/off.

It's practically flicker-free from 100% down to around 25–30% brightness (Below that, there’s some PWM, about 60Hz range)

For best results,

Keep brightness around 40–80% (to stay in DC dimming range), Use True Tone off, Red Filter ON and Reduce White Point (30–40%)

Also, the iPhone 11 is LTE-only

which means there is NO 5G, it's a huge deal in itself.

TL:DR;

If you're flicker sensitive, iPhone 11 is your best apple option currently.