DecaHertz
Very similar to you, in that in almost all cases I can only use (some) TN displays and have essentially never had a good experience with IPS.
(Out of all of the IPS displays I've ever used, only one single old IPS laptop I could actually be productive on, and even then it still had strain when compared to my current TN setup. Also, there are still some TN displays that strain me as well)
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My current TN display that is working great for me is this: https://www.panelook.com/B140XTN02.D_AUO_14.0_LCM_overview_26816.html
It is WLED backlit, but is currently the device I am the most productive on, and I feel fine even if I use it for hours every single day.
Note that to make the screen's output "perfect", at least on an Intel UHD 620 graphics laptop, it has to be run under Linux with specifically the legacy unaccelerated "Vesafb" framebuffer driver, and kernel modesetting disabled.
If I run it under the newer "Uvesafb" instead which requires kernel modesetting, any Intel graphics driver, or even Basic Display Adapter Windows, the output is much worse — even though it's actually still a lot better than other screens, I experience some of the "unable to concentrate" you're describing (and mild strain).
But, if I use the "Vesafb" driver, the image is nearly perfect to my eyes and I don't experience any strain!!
Even before I found this strategy, the panel already looked perfect in the laptop's BIOS, but not when booting into an OS.
I'm not sure what's different about using Vesafb, but it essentially seems like it's doing something that maintains the same "unprocessed" output and comfort of the BIOS, even after booting into Linux and switching to the native resolution.
And this is how I'm now able to use it CONSISTENTLY every day for the past 3 months. I can finally enjoy using a laptop again and text is soooooo easy to read on my current setup.
Still trying to come up with an reproducible step by step guide that works on a mainstream Linux distro to create the same setup that I've managed to achieve with this panel — when I do, I will share it on this forum. Probably in few months from now.
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BTW, I did find recently that some VA screens are OK for me as well — specifically, really old Sharp VA TVs from the 2000s with their own variant of VA called "ASV Black TFT". Those screens are good enough where now I use a Sharp LC-G5626U from 2004 pretty frequently as an external monitor.
The Sharp has a CCFL backlight, but given that it's pretty similar to the AUO TN panel in comfort to me, I don't think the backlight is the main factor in my case.
(The Sharp does require certain hardware to output the best possible image though — I've only gotten output on the TV to look equally as crisp and comfortable as the TV's built-in menu with a first generation Raspberry Pi from 2011 connected.
Connecting a regular PC instead, including Intel Graphics, NVIDIA or macOS devices, sends a noticeably different image that isn't comfortable to look at and looks hazier/blurrier than the TV menu — even if I select the same resolution, disable dithering, etc.
Fortunately, I can run a VNC client on the Pi and connect to my other PCs from the TV that way. And even though I'm remotely viewing the same desktop, the output looks so much nicer to me than trying to connect one of those PCs to the TV directly.
The fact the same desktop looks OK when viewed through the Pi, makes me think that in this case, the GPU of each PC is the problem, not something easier to explain like simply the text rendering of the OS etc.)
I don't think I'd have much luck with other brands of VA panels though, as other VA types seem pretty different in how others have described them.