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.

Don't use anything with alcohol, ammonia, or solvents because they damage the OLED screen coating even in small amounts. The best thing is a dry microfiber cloth or one slightly dampened with distilled water - you wipe it very carefully without pressing, and that's it. I've got several plants at home and I'm pretty careful with my stuff (the job helps with that too), so trust me when I say the simple technique is always the best way to not risk anything.