Is it possible to mute notification sound on ALL apps? I want to enable the sound button (left side of the iPhone X), but then I got the notification sound whenever I got a message on WeChat. I'm fine with disabling the notification sound on WeChat. 

But then, there are other, numerious apps that send out the notification and whenever I get it, the notification sound is alerted.

So far I only found it is possible to disable the sound one by one on each app, but is there any global setting that disables it? I use iOS 11.
No.

Unfortunately, there is no way to do them all at once. You’ll have to do them individually.