Takes2-2tango: Music is the language of the soul, when you listen to it you literally fall into the world of whoever created the music, into their soul. I believe Rabbi Dessler (I don’t remember which Rabbi it was) has an entire explanation for how it works. Music is extremely powerful.
If we are going to go the route that even though many Rabbanim say it’s horrible for your neshoma, some disagree, than first we have to cut out most of the rock and pop music. Any music that makes you feel like you should dance in a not tzniyus way.
Music should be something that connects you to HASHEM. You should be able to listen to a song, and afterwards be able to daven 5 minutes later. Try listening to a non-jewish song and davening right after and see where your head is during davening. I’ll bet you many songs will put your head is not good places.
Beyond that Midwest2 says you can listen to clean romance. According to many rabbanim any romance music, anything written from a man to woman or vise versa is assur. It violates the prohibition to listen or say nivul peh which according to many poskim is anything that is meant to be between a man and woman.
There’s many opinions, and I cannot judge anyone here for whatever theirs is. I assume they had a start conversation with their Rabbi and are following his advice on what is allowed and what isn’t.