Saw you posted in my thread but since you have a specific issue here I'll go into some details to what I did (and found).
1. First problem was I wasn't using the proper cable (you say not an issue for you but just an FYI to others looking at this post) in that I had a DP cable but not one that could support the resolution
2. Acclimation for me took a few days - at first I toyed with the settings and I used the settings found here (https://www.tomshardware.com/reviews/asus-rog-strix-xg35v-curved-monitor-freesync,5529-2.html) to set everything but I was conflicted on the brightness and couldn't find a good explanation online on what I should do
3. Brightness I ultimately just used a light meter app I have on my phone for photography to figure out what the brightness of my desk was and then matched it to what TH had and I found that I went with the Brightness 80cd/m2 setting.
4. Ultimately even after I put in the monitor, fixed the cable, set it where I wanted it, and got the brightness it still took a few days after that for my eyestrain headaches to go away. I choked it up to needing to acclimate to the wider screen (I came from 2x 23s) and the curved aspect of the screen as well as the brightness setting.
5. I too thought about boxing it up and returning it, actually I was very frustrated with #1 because there's barely any info on this monitor and I wasn't seeing any help online whatsoever. I randomly just Googled "Max resolution HDMI cable" or something to that effect and saw that the max was 1980 wide and realized that the monitor wasn't busted but my stupid self was using the wrong cable - so I went to the cables that came with this - solved Issue #1 but it was super frustrating that I couldn't find squat online.
I would say give it a few days after you get everything set - how it should be. I will say for me it's very crisp both with my work laptop (using HDMI cable that came with it) and my desktop (using the DP cable that came with it) and the colors are very nice. Once I solved the initial cable issue that made a huge difference (it was unusable until then). After that the brightness was the big one for me and it took some time to acclimate to but now I can sit in front of it for hours upon hours upon hours.
Here's my settings if anyone is curious or needs some help:
- Game Visual = Racing Mode
- Color =
+ Brightness = 6
+ Contrast = 80
+ RGB = 100/100/93
+ Gamma - 2.2
- Image -
+ OD = Level 3
+ Adaptive-Sync/FreeSync = On
+ Blue Light Filter = Level 1
+ Shadow Boost = Level 0