Reverse only touches the selected clip. That gives you a few options for sound:
Music on its own track
Music added from CapCut’s sound library, or as a separate audio clip, isn’t reversed. Reverse the video clip and the song plays on normally.
The clip’s own sound
A clip’s own audio is reversed along with its picture. To keep that sound forwards, select the clip and use Extract audio before reversing, so the sound sits on its own track; then reverse the video and mute the clip itself. In the browser reverser, the same result is one switch: turn Sound on and Reverse the sound too off.