"3kHz is still in the range of flicker sensitivity for humans.
OLED has 2 issues, which make me hesitant to recommend to people:
1.) PWM brightness dimming flicker
This is the part that's advertised as 3kHz. Most smartphone exhibit this, even at 100% brightness sadly) as a power saving measure.
I've personally had issues with 2.5kHz - 3kHz PWM brightness dimming flicker on LCD displays, hence why I said it's a band-aid. It reminds me of this great quote from Malcolm X:
“I will never say that progress is being made. If you stick a knife in my back nine inches and pull it out six inches, there's no progress. If you pull it all the way out that's not progress. The progress is healing the wound that's below, that the blow made. And they haven't even begun to pull the knife out, much less pull, heal the wound... They won't even admit the knife is there.”
The same can be said for PWM. It needs a drastically different approach to not be an issue.
Take a look at this explanation to understand why the PWM value should either be 0 (no major variation in brightness) or a much larger value: https://forums.blurbusters.com/viewtopic.php?t=6519
2.) Refresh rate brightness dip
There seems to be a ~25% brightness drop every refresh cycle, which can be a contributor to eyestrain as well.
This seems to be a inherent hardware design of current OLEDs, regardless of TV, smartphones or desktop displays. The actual reason behind it, I haven't been able to find out. I've seen theories thrown around, such as this being an issue with the nature of capacitors (not fast enough to empty/fill themselves) but I haven't come across nothing conclusive.
That's why I refrain from recommending any kind of OLEDs displays for now, until these 2 issues are resolved.
I don't think anyone should try to forcefully "adapt" themselves to OLED. All humans show sensitivity to flicker, whether they perceive it or not. It's better to just opt for a safer IPS LCD phone.
As for your Xiaomi dilemma, it seems that the 14T Pro has both of what I've mentioned.
https://www.notebookcheck.net/Xiaomi-14T-Pro-smartphone-review-Amazing-value-amazing-screen-brightness.907877.0.html
This can be easily seen in Notebookcheck's review.
Yes, OLED's and smartphones as a whole (due to heavy RF emission) can cause "sick feelings" and dizziness.
I haven't seen people mention the neck symptoms however.
You could consider doing neck exercises (basic neck extension & flexion, 3x a week, be extra careful & slow when performing them) for overall wellbeing.
Hope this helps."
https://www.reddit.com/r/PWM_Sensitive/comments/1fr8444/comment/m08to38/