DishaSamir It depends on your budget and what preferences you have
Eyestrain is very individual sadly, so, what may work for some may not work for other!
From PWM (flicker, motion artifacts from PWM), LCD inversion artifacts, motion blur, AG coating, polarizer, brightness, color gamut, dithering to improper posture, stress, not using eyeglasses and using monitor too close to the eyes, a lot of factors are in play!
You should mention what displays you've had success with and which ones didn't work for you, to narrow down the choice!
To minimise the most common culprits of eyestrain, you should consider getting a reviewed monitor (perhaps from r/monitors discord recommendation list)
For 1080p (24"), I'd recommend:
• Dell S2522HG [240hz],
• Viewsonic XG2431 [240hz],
• AOC 24G2ZU (24G2ZE) [240hz],
• Asus VG259QM [240hz],
• MSI MAG251RX [240hz],
• Dell AW2521HF(A), [240hz]
• Omen X 25 [240hz],
• Omen X 25F [240hz],
• AOC 24G2U [144hz],
• Gigabyte G24F [170hz],
• BenQ EX2510 [165hz],
For 1440p (24-27", 240hz - 165hz), I'd recommend:
Asus PG279QM [240hz],
Asus XG27AQM [240hz],
Alienware AW2721D [240hz],
Gigabyte M27Q-X [240hz],
Omen X 27 [240hz] (beware, this one has PWM at ~2000Hz, as measured by RTings),
Del S2417DG [24" 165hz TN, ~120ppi and good response times, discontinued tho I think],
MSI Optix MAG274QRF-QD [165hz],
LG 27GP850-B / LG 27GP83B-B, [144hz]
Dell S2721DGF(A) [144hz],
LG 27GN800 [144hz]
HP X27q [144hz]
Dell S2722DGM [144hz]
For 2160p (4k 27"), I'd recommend:
• Gigabyte M28U [144hz],
• Gigabyte M32U [144hz],
• Acer XV282K KV [144hz],
The higher the refresh rate, the better (especially if the the response times are in the refresh window) the motion performance, which is something everyone should strife for (especially if eyestrain is related to motion blur, as I've noticed a lot of members of this forum have very bad performing monitors)
There's a compromise between PPI (pixels per inch) and high refresh rate however. The 1080p monitors are still overall faster than most 1440p monitors at the same refresh rate. 4K can't compete yet, as 240hz 4k isn't out yet (on a flat monitor, I don't count the Neo G8, even though it's a monster in its own class)
DisplayHDR400 is also a certificate you could keep in mind, it is a sign that the monitor is 8bit capable, avoiding dithering (even though I'm very sure there's only a ~1% change eyestrain is related to this)
Keep brightness at around ambient levels, you don't need to enforce 500 nits (cd/m2) in dark rooms, try aiming for 50-200nits for daily usage (and try looking for a Freesync / Gsync certificate, it's a sign the panel is using DC dimming, not always though but 95% of the time it's right)
If you don't want blue light affecting your sleeping schedule, consider investing in blue light glasses to remedy this (there are also a few studies linked to worsening of eyesight when exposed to blue light with continuous use) or use the in-built blue light filter found in monitors above.
Personally, if it was strictly for gaming, I'd go for 1080p 240hz (the first 3 models) or some 1440p 240hz model if your budget allows for it, as I find anything below (without strobing / motion blur reduction / single-strobe PWM, so sample and hold basically) 240hz to be very unsatisfactory when it comes to motion blur management.
I hope I've managed to narrow down the wide choice of monitors.