X230 IPS Screen Causing Eye Strain

I recently purchased a refurbished X230 with an IPS screen (panel model according to HWiNFO: LP125WH2-SLB1). I found out that X230 uses PWM to control the brightness of the screen and that too a very low frequency. I used to get headache and feel nauseous within thirty minutes of using the laptop. Then I found out that there is a way to increase the PWM frequency. Now I run the screen at 20 KHz (default is 220 Hz) at all times. The headaches and the nauseous feelings have gone away, but I still find the screen extremely uncomfortable. I can't explain the problem in one sentence, I will do my best to explain in a few. I find it very difficult to focus on text, especially light text on dark background (I am a programmer and I use a dark theme wherever I can). It's like I have to put in a lot of effort to focus on text, which tires my eyes over long periods of continuous usage. I tried reducing the contrast and brightness, makes no difference. After a while of reading text, if I close my eyes or look at a white wall, I can see horizontal black bars as an after image. I also find the screen to have this strange glow which tires my eyes, especially when the background is white (I know this sounds stupid, but I am just describing what I feel as best as I can). I also found out that LP125WH2-SLB1 panel has bad ghosting and backlight bleed issues and I confirm that my panel has them as well, but I feel they are not contributing to eye strain, though I might be wrong. I use flux at night, and strangely, I find the screen much more comfortable to use with flux.

Now, I have researched as best as I can on these problems. Some say that some people might find IPS displays uncomfortable at first and then they slowly get used to it. I gave it time and I am not getting used to it so this solution can be rejected. I have been using an Ideapad with a ****ty TN display for the last six years and I never had any eye strain issues with that panel.

I also read that LP125WH2-SLB3 and LP125WH2-SLT1 panels are supposed to be better than LP125WH2-SLB1, but the reviews on the former panels are mixed. Some even say that there are newer LP125WH2-SLB1s out there that are better than the older LP125WH2-SLB1s, whatever the **** that means. So should I try replacing the panel with either SLB3 or SLT1 as a last resort? X230 is an amazing machine which is why I am trying so hard to find a solution so that I can continue using it. I hope you guys can point me in the right direction.