Diagnosis
QLED screens have a special anti-glare and anti-reflective coating that can be damaged by household cleaners, ammonia, or alcohol. Using the wrong stuff will create permanent smears or dull spots.
How to Fix It
The only safe method is a dry microfibre cloth first. Use a clean, soft, lint-free cloth (like the one that came with eyeglasses) and gently wipe in one direction to lift dust. For fingerprints, you need moisture, but not a spray. Dampen a second microfibre cloth with distilled water only. Wring it out completely so it's barely damp. Gently wipe the screen, then immediately follow with the dry cloth to buff off any moisture streaks. Always turn the TV off and let it cool first so you can see the smudges better.
If That Didn't Work
For stubborn spots, you can use a 50/50 mix of distilled white vinegar and distilled water. Again, apply it sparingly to the cloth, never directly to the screen. Vinegar is a mild acid that can cut grease but is less harsh than chemicals. Test a small, inconspicuous corner first.
Heads Up
Never use paper towels, kitchen roll, or rough cloths—they will microscratch the coating. Never spray anything directly onto the screen, as liquid can seep into the edges and damage the panel. Pressure is your enemy; use a light touch.