The radio in my 2015 Hyundai ix35 has lost all sound

I’m not sure that this is a common fault, but it’s certainly not unheard of. The stereo in a modern car is like any other electrical appliance; it has the potential to just up and die for no good reason.

But rather than simply replace the unit you have, why not shop around for an improvement. There are many, many, aftermarket stereo systems that will fit your car and will have superior Bluetooth functionality and more features than the stock head unit from 2015. You might find they’re cheaper, too.