They say that listening to music on headphones while walking is harmful. Is this true, if so, how does it affect the body?

To listen to music specifically when walking is harmful in one case: you can cross the roadway and simply not hear the car honking. Such cases are a dime a dozen, just like at a railway crossing.

Pulling bananas from your ears for 10 seconds can save yourself 70-80 years

Listening to music with headphones is generally harmful. Even lying down. And in general, listening to music is harmful. As well as breathing.

I once broke my nose on the street when they tried to gop. All because I was walking in headphones and did not hear the polite request for a light.