I use a 6 plus which doesn't bother my eyes and a buddy of mine came by who has a XS Max. He let me take a careful look at it- in the dark.
Holy crap the flickering from that OLED screen is atrocious. Clearly visible strobe effect anytime my eyes moved quickly by the screen. Straight on and especially in my peripheral vision. It looked like those horrible flickering tail lights on Cadillac Escalade vehicles.
I literally couldn't allow my eyes to get anywhere close to that flickering piece of garbage, even peripherally. Way too stroby for me.
I asked him if his screen gave him eyestrain or headaches and he said no, yet I couldn't get within two feet of it (in the dark) without it really messing up my eyes.
So for me- Apple's OLED screens are hazardous garbage, yet for others, they're fine. So you've got to try out different screen tech (LCD vs OLED) on your own to see what bothers you and what doesn't.