Mike Russell is an audio expert with some great tutorials. Here is a superb example of how to mix a voice over with background music without ducking the music volume.
We don't know where to begin with Mike Russell's channel, because it contains an absolutely vast amount of knowledge on how to achieve various things with audio. Everything from sweetening voice overs to the correct way to remove background noise is covered.
Be warned, these are in-depth tutorials and some of them do use some specialist tools, but having said that they are a good lesson in how to professionally isolate various audio frequencies and work with them to get the best result.
The video below was made in 2017, but covers a topic that is no less important now. All too many people rely on audio ducking to make their voice overs stand out over music, and whilst that is a good basic technique, there are better ones, such as isolating various competing frequencies and reducing or boosting them.