My iphone xs max has gone to black screen and will not turn b

Hello,

Take a look at this arctice:

If your iPhone, iPad, or iPod touch won't turn on or is frozen - Apple Support

I had this problem too so I tried to update to iOS 12.1; first over wifi and then connected to iTunes. Now my phone is stuck on the screen showing the cable connecting to iTunes. I tried the hard restart with no luck. I live in Hungary and can't just go down to an actually Apple store.

Sorry - my response duplicated Gus' previous response which I had not seen.

Hi

Press the side volume button up quickly then side volume button down quickly

Then press & hold power button down until you see apple logo.

Cheers

Brian 🇬-1F1E7;

Oh no !! I feel for you my friend !! My advice - call apple tech support ASAP !! Right now !!! 1800 6927753