It's noisy upstairs next door! Is it useful to decorate the soundproof wall?

The general sound insulation wall has some effects, but it will not be better than earplug earmuffs. Tens of yuan/square is nothing more than sponge or asbestos lining, which is not good for health. Professional ones are extremely expensive. I suggest you complain to the landlord and property management. If not, call the police. Not yet. I'm afraid you should consider moving.