Made an account just so I could leave messages about this. I've had my 12 mini for two days and since the first night of using it I felt a strain headache across the top of my forehead/sides of head and dizziness, the only way to describe it is like slight motion sickness.
For me, it is worse when I'm scrolling on text or instagram for example, as it scrolls up it makes me feel dizzy, like motion sickness like when you come off a ride. I've come straight from an iPhone6 to this so not sure if it's the longer screen dimensions and it will take getting used to, it feels like it's scrolling too quickly for my eyes and my eyes can't get from the top of the screen back to the middle again in time.. I've had iPhones since the first one and never had an issue before.
I normally hold my phone quite close, imagine sitting down, my phone would be parallel to my chest. If I hold this 12 mini there, it strains and pulls my eyes, and feels almost fisheye looking, I have to hold it further away, parallel to my hips almost.
I've changed white/brightness, turned off face ID etc, didn't make much difference.
I'm writing this on my laptop as I've lost any desire to even use this phone, it irritates me just being around it, unless that's subconsciously at the amount I paid for it. Not impressed. Very much considering getting an SE2 or an 11 that still have LED screens, honestly miss my 6 after this.
Anyone reading this who hasn't left a comment, I urge you to so they get more feedback on it and hopefully do something about it.