Natural product to clean smart TV screen without damaging it?

The safest thing is to use a slightly damp microfiber cloth with distilled water, you don't even need any products - that's what most manufacturers recommend for OLED.

If you have stubborn marks, you can mix distilled water with a bit of white vinegar, but make sure you wring out the cloth really well before wiping the screen so it doesn't get too wet.

Completely avoid alcohol, regular household cleaners, or anything abrasive, because they'll actually damage the screen's coating.

Distilled water with a drop of white vinegar works well and is completely natural, you just have to be careful to keep the cloth damp but never soaked - excessive moisture is what really damages OLEDs, even if it seeps in through the edges.

Wipe with gentle movements, no pressure, and let it dry completely before turning it back on. Forget commercial products, this does the job and saves you money.