For me, I don't get immediate symptoms from PWM (it takes about 20 minutes to feel it), however, if a device has that specific kind of "fake 3D" feeling to its display output I get symptoms and brain fog immediately.
Devices with really strong PWM can certainly be really straining and painful to use for too long, like an old CRT — but… I can tell that's an entirely different kind of strain compared to the even worse type of eye pain + constant double vision that I think is induced by color and contrast post-processing that can totally disable me and prevent me from concentrating or smoothly reading, even on devices that are otherwise PWM-free.
I'm unsure about temporal dithering, because most screens and devices affected by dithering also have many other issues related to post-processing.
Even an ancient CCFL TN 4:3 monitor from 2005 I own, which also uses temporal dithering, adds really obvious "extra" white halos around all text regardless of what device is connected.
I definitely feel a decent bit better after disabling dithering on devices — but as long as there's no strobe-like PWM which causes its own set of issues, it really seems like it's way more about the colors and amount of post-processing that makes or breaks a screen for me (compared to the temporal element).
One example is my single "perfect" laptop, which still has a mild flicker depth version of PWM (looks more like incandescent flicker instead of fluorescent flicker in a slow motion video), and potentially has some pixel flicker and pixel inversion too, because it doesn't feel as still as e-ink. It's even WLED-backlit and not CCFL!
BUT… despite all of this… I can use that laptop perfectly with nearly no Issues, no other laptop screen I've tried yet even comes close to how good this one is.
When I look close up at the pixels on that one laptop —at least while running the specific Windows 8.1 version that's currently on it — it's apparent to me that the amount of post-processing is very minimal, compared to bad screens where I immediately see e.g. obvious halos, blue and green glows around contrasting objects, and "extra red color fringing" everywhere.
Side note, the pixels on my 2004 Nintendo DS top screen (interestingly, not the bottom screen, which does cause some mild strain) look even more "pure" and unaltered compared to the laptop! I notice essentially zero post processing or anything resembling edge enhancement on that DS top screen! However, the specific old laptop is already "pure" enough to cross that "perfect screen threshold" for me, which very few devices have achieved.
It really seems to be connected to the "simplicity" of the output on each, the pixels are displaying something very precise to the exact unprocessed colors that would appear in a PNG screenshot, and doing very little "extra", e.g. colors seem to not be "leaking" in a fuzzy way into nearby pixels.
What I think the solution is:
Therefore, I think the longer term solution truly lies in figuring out how to build a custom LCD controller, TCON, driver board from scratch that ensures the signal it receives is reproduced as purely as possible, skipping every possible enhancement, to the point where doesn't even do any gamma correction or color calibration —
(of course, also connecting it to a safe GPU, or even better having the computer just take constant "simple" screenshots like VNC and then transferring it to the controller in a different way like USB… similar to how DisplayLink works.)
I feel like this side of the hardware is way more important to put the effort into trying to redo from the ground up… compared to building a new type of physical pixel or backlight module, but then pairing it with a generic off-the-shelf controller board that still creates "bad output", such as dithering, inversion, messing with colors/contrast/edges, oversharpening…