Diagnosis
The monitor has a standard matte anti-glare coating. Using incorrect cleaners or abrasive materials can permanently smudge or damage this coating, creating shiny patches.
How to Fix It
Power off the monitor and let it cool. Use a dry, soft microfiber cloth (like for glasses or cameras). Gently wipe the screen in a circular motion to lift dust and oils. For stubborn smudges, lightly dampen a second microfiber cloth with distilled water. Wring it out completely so it's only slightly damp. Wipe the screen, then immediately dry it with the first dry microfiber cloth.
If That Didn't Work
For persistent marks, use a screen cleaning solution designed for monitors or LCD/LED TVs. Spray the solution directly onto the microfiber cloth, never onto the screen. Avoid solutions containing ammonia, acetone, or ethyl alcohol.
Heads Up
Never use paper towels, kitchen towels, or tissue. They contain wood fibers that will scratch the coating. Do not apply pressure; let the cloth do the work. Avoid cleaning the screen when it is warm from extended use, as this can streak the coating.