I have the same on some of mine...a result of winter injury/freeze. Still good tissue on the opposite side and wound can heal in a little over time, [I see a little top left] if not too bad. Time will tell how long it can hang on.. you can peal off the dead bark.

Your tree appears to be very badly deteriorated with dead bark and a large dead stub where a branch had been cut off. Apple trees can often continue to produce fruit even when in bad shape as in the case of your tree, though I'd look to get this tree grafted onto a healthy new rootstock if you wish to preserve the variety you have there.