Is it fine to charge my iPhone with MacBook adapter 96w

Watt  is like how fast your car can drive, but the speed limit is how fast your car do drive

the iphone draw as much current as it was build to use when charging, the fact that a charger can provide a lot more just means it's not having its full capacitive used

so as long as it's no higher than 5volts and the connector fits and it's minimum 5 watt then it could be 5GigaWatt without problems